Fix an omission in French localization
Fix editing of name of Open Reader feeds
Use user's preference for detecting a double-click
Further tweaks to User-Agent

Follow-up on issue #215 :
- default user agent will now be similar to : `Mozilla/5.0 Vienna/3.0.0`
- browser panes' agent will be similar to : `Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_2) AppleWebKit/537.74.9 (KHTML, like Gecko) Vienna/3.0.0 Safari/537.75.14`

Therefore, the browser panes User-Agent is more similar to Apple Safari's. This way, sites like iMore.com will not nag us anymore that we are using an outdated version of Safari.
Note that the first part of the browser pane User-Agent (which quotes Mozilla/5.0, OS X version and WebKit version) is automatically added by WebKit.
Encode URLs sent to plugins

Solves issue #258

Note that links from browser panes are encoded once, and links from articles list are encoded twice.
So a non-breaking space (byte sequence C2A0) becomes %25C2%25A0
Fix an exception to UnifiedDisplayView
Change a text in appearances preferences

Changed in English and in French :
"Show feeds icons in folder list" instead of "Show folder images in folder list"
Merge pull request #267 from barijaona/bugfixes

Various bug fixes and improvements