Add donation popup

[Popolechien]

Signal has a donation prompt that appears every three months or so at the bottom of its android app. Nothing fancy (see text below - it's in French but the gist of it is Donate today / Signal needs your help with the choice button being remind me later of donate)

There is already a static feature in the settings, so this is in addition to the latter.

Signal has a sophisticated donation funnel that allows in-app payments, but at this stage a link to support.kiwix.org would already be good

[kelson42]

@MohitMaliDeveloper Please implement something like in Signal.

[kelson42]

The donation does not look well on tablet in dark mode, please make abetter proposal.

[MohitMaliFtechiz]

@kelson42 For tablets we can show this in the middle with half of the screen size width, and when the tablet is running in portrait mode we can show the the donation dialog something like this. @kelson42 What do you think?

(Device width/ 1.5)	(Device width/ 1.2)