Add a configuration option to get sticky articles

Now the user can choose if an opened article will be repositioned to the top or not

See #338
Merge pull request #435 from aledeg/issue338

Add a configuration option to get sticky articles
Alpha version of Google Reader compatible API

https://github.com/marienfressinaud/FreshRSS/issues/13
Hardcoded passwords, no possibility to add/delete feeds or edit
categories yet.
API: default link to compatibility check

https://github.com/marienfressinaud/FreshRSS/issues/13
API: Better temporary security

https://github.com/marienfressinaud/FreshRSS/issues/13
Slightly better security while waiting for a proper authentification
system
API: sanitize username

https://github.com/marienfressinaud/FreshRSS/issues/13
API streamContents for categories and feeds

https://github.com/marienfressinaud/FreshRSS/issues/13
API: Real password system

https://github.com/marienfressinaud/FreshRSS/issues/13
Expiring token not implemented yet
API: SQL optimisation

https://github.com/marienfressinaud/FreshRSS/issues/13
Show only unread when selecting unread

Before, when there was no unread articles, all articles where displayed. This behaviour was not the one intended.
Now, when there is no unread articles, a message is displayed to alert that there is no article.

See #428

Correction after comment
Merge branch 'issue428' of https://github.com/aledeg/FreshRSS into issue428

Conflicts:
	app/Controllers/indexController.php