Move update icon and update icon blinking to css

Use CSS3 Animation for the "loading icon" blinking and move the definition of
the loading icon to CSS as well.

CSS3 Animations are supported by IE10, Firefox and using the -webkit prefix by
Chrome and Safari.

I've dropped the usage of element.classList in favour of supporting refreshing/
article downloading in IE9 (again). The classList stuff isn't necessarily
needed, as the elements in question only get one or no class assigned.

I've dropped no longer supported css options like:

the appearance option isn't supported by any browser, the -webkit-appearance
doesn't change anything visible.

-webkit-font-smoothing support was dropped in chrome 22 and font-smoothing
isn't specified anywhere.
remove multiple definition of data-item-page
Fever API: Allow to select the database

Utilize apaches mod_rewrite to append a database parameter to the fever
api script based on the requested URL. Basically everything after
/fever/ is treated as the desired database. E.g. using
https://www.miniflux.net/fever/custom.sqlite/ as server url selects this
database as sync source/target.

The user supplied database parameter is compared with the output of
Model\Database\get_all(), which ensures that only files within the
DATA_DIRECTORY can be referenced (prevents File Inclusion/Directory
Traversal vulnerabilities).

I've tested it against Reeder on iOS. Note that Reeder does not allow
the same user name to be used multiple times within the same domain
name, even if the used URLs are different.
fix RTL toggling

H2 within an item preview was toggled to rtl and back to ltr
immediately.
Fix a bug for image proxy and update dependencies