Adds tabindex to file icons so they can receive keyboard focus. Pressing Space
while an icon is focused brings up a menu where the folder to move to
can be selected.

Also adds "Folder:" text to folders in the file browser and adds accessible text
to parent folder links.

Change-Id: I29ff9733f79478dc1724fe0c579bbfa2e9b74ad0
Signed-off-by: Jono Mingard <jonom@catalyst.net.nz>