Add the ability to hide a calendar

[Benjamin-Loison]

Like Etar Display events:

on LineageOS 23.2.

My current workaround consists in using the Firefox uBlock rule:

##:xpath(//div[contains(@style, "background-color: rgb(139, 195, 74);")])

with the color being unique and associated to this calendar.

On Debian 13 GNOME and Linux Mint 22.3 Cinnamon.

Personal notes:

Benjamin_Loison/etesync-web/issues/37