feat(meta): add extension icons for all the browsers

Use the "happy" icon as extension/add-on icon for every browser.

This closes #32.

Yay!
feat(settings): remove donation links, rename "Help" to "Backup"

Remove donation options from "Help" settings section.
Then rename "Help" section to "Backup" as backup options
are all what remains there.
See #134.

This closes #134.
chore(changelog): en, ru
chore(release): 0.5.0