Add Block-All mode

[smalluban]

Adds Block-All mode toggle to the trackers page.

Switching it on:

• disables TrackerDB DNR ruleset
• Forces isCategoryBlockedByDefault to return true

It means that TrackerDB is removed from allowing/blocking anything by default (if there is no exception on the tracker).

The copy needs a review, it is made by me ;)

[github-actions[bot]]

Builds for commit 4408480ce3b9fa745bce83b991f2f1aeeee4f26d:

• ghostery-chrome-10.3.7-923767f
• ghostery-edge-10.3.7-923767f
• ghostery-firefox-10.3.7-923767f
• ghostery-opera-10.3.7-923767f

[GRadziejewski]

Checked and, in my opinion, it works good. No breakage spotted (checked with a few commonly visited pages.