Tweak some styles in AppDetails2

Merged username-removed-25042 requested to merge pserwylo/fdroidclient:new-ui--app-details-2 into master

Identified a bit of low hanging fruit for brining the new AppDetails2 screen more in line with that of #749 (closed). Will need to make some better buttons for Bitcoin/Flattr/Litecoin - but that should be straightforward to replace as they are just drawables in the res/ directory.

Current view:

current

New view in this MR:

new