Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>

If a room is associated to a file now an icon is shown to the right of
the room name; when that icon is clicked the Files app is opened in a
new tab and focused on the file.

The "Go to the file" hint is shown using the tooltip plugin instead of
the link title for consistency with other buttons in the UI, and because
it is automatically shown when the icon is focused while traversing the
UI elements with the tab key.

The icon has a clickable area of 44x44px; due to how the properties for
h2 elements are defined in the server some margin juggling is needed to
vertically align the icon with the room name header.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>

In the server, ".icon-file" is set to the "text" icon instead of to the
"file" icon. For consistency with the server and between the room list
(which uses ".icon-file-white") and the icon to go to the file (which
uses ".icon-file") now ".icon-file-white" uses the "text" icon too.

Note, however, that the icon for shared files that do not have a preview
is still the "file" icon, as in that case it should reflect the file
contents and using a text icon for other types of files could be
misleading.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>