clean up various L10n strings

[cvan]

Fixes #648

• always use curly quotation marks when appropriate
• merge voice_search_example into voice_search_start
• add strings for Bookmarks
• add strings for Tabs
• add strings for Downloads
• add strings for History
• add strings for Settings changes
• add strings for Keyboard changes
• add strings for tooltips (see designs, from Add Tooltips across the UI #365 (comment))
• review any missing strings from old Design Review decks
• verify descriptions and STRs of L10n comments

@Delphine

[Pike]

I've just given this a really cursory glance. This needs an actual review by someone who's not already having the next day.

[Delphine]

Gave a first past at this. Same comments as Pike + some more.
Also, are we sure all the instances of %1$s should be replaced by domain name instead of app name? Some of these look strange to me (only called one out by looking again, others look like that too).
Probably just best to double check. Thanks!

[Delphine]

Ok I think we're almost there.
Just wanted to make again extra sure all the instances of "'%1$s' will be replaced at runtime with the website's domain name." should in fact be "website domain name" and not "app". Sometimes it feels like we're more talking about the app, but then again, I don't know :)