Google Calendar Weekend Highlighter

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   Changelog:
    
    - 1.0.1: Added colour sample cell on the right of colour selector.
    - 1.0.2: Correction of bad version upload.
    - 1.0.3: Manifest update. Simplified script code with bug correction:
             script did not fire correctly at the end of DOM loading.
    - 1.0.4: Google inserted funny hidden fields in calendar Week View, and 
             we needed to skip them for correct highlighting; this is just
             a bug fixing release for that purpose.
    - 1.2.0: COLORIZATION METHOD REDESIGNED:
             Now this extention can colorize also the CUSTOM calendar view!
             No matter which "period" you will choose, from 2 days to 3 weeks, 
             GCalColour will light up your weekend! :)
             NEW FEATURES!
             Asked by many, now you can choose the weekend days of your own country!
             Just open the options and write in the textboxes the short name 
             (three characters) of your two weekend days (SAT-SUN, SUN-MON...).
             Just write the "day codes" in the language with which the browser works.
    - 1.3.0: Extension Rename! There were already some junk extensions out there 
             with the same name as mine, so I decided to rename it.
             ADDED COLOUR PICKER
             SLIGHT CHANGES TO OPTIONS PAGE
    - 1.4.0: Now works with all possible layouts of Calendar, except for "Year layout"
             (in that layout weekend colorization is pretty pointless)
    - 1.5.0: Added initial check of options, for dummies.
             If user has not set custom weekend day labels yet at load, 
             the extension automatically brings you to the options page where
             you can do your customization (colors and labels for weekend days)!
    - 1.6.0: Added dropdown for weekend days choosing, added loop to force user to 
             select weekend days.
    - 1.7.0: Added language in the options. This is necessary for users 
             that have browser "preferred language" that is not in the first 
             place in the list of the browsers languages.
    - 1.7.1: Solved a bug that prevented the "customweek" view to work
             (thanks to user Amir Yabo for reporting!)
    - 1.7.2: Minor changes to options page.
             Added a link to all my extensions in the extension's context menu
    - 1.8.0: Migration to Google's Manifest V3 for extensions
    - 1.9.0: Bug fix
    - 2.0.0: DRUM ROLL... COMPLETE CHANGE OF PARADIGM!
             Now you can choose a CUSTOM COLOUR for EACH of your week's days!
             Yay!!! :D
             You will be redirected to options page again, after 
             upgrading to version 2, because there are a lot of days more 
             to customize. If you want things to work like before,
             simply choose the same colours for your good old days, and
             leave in WHITE the other days (that's the default by the way)! :)
             Enjoy!
    - 2.1.0: Google changed the code of Calendar's pages! So I needed to 
             re-adapt the DOM interpreter. Now the extension works again
             as expected! ;)
    - 2.1.1: Another change Calendar's pages CSS, and another little change in
             DOM interpreter.
    - 2.1.2: Another change Calendar's pages CSS, and another little change in
             DOM interpreter.
    - 2.1.3: Another change Calendar's pages CSS, and another little change in
             DOM interpreter.
    - 2.1.4: Another change Calendar's pages CSS, and another little change in
             DOM interpreter (no, I'm not stuck in a loop, this is Google's 
             bad habit to change things in CSS without need!!!!!).