pakfire.cgi: Convert icons to buttons.

pakfire.cgi: Convert icons to buttons.

- Convert icons to buttons on main and confirmation pages.

 - Disable Upgrade button if no core or add-on updates available.

 - Disable Install and Remove buttons until an add-on is selected
   to install or remove.

 - Change 'abort' to 'cancel'.

 - Change 'uninstall' to 'remove'.

 - Set fixed height on select boxes to keep the size the same if
   there are no options for the select.

 - Change translation for install/remove description text, the previous
   text referred to the icons.
     'pakfire install description' -> 'Please select one or more add-ons to install.'
     'pakfire uninstall description' -> 'Please select one or more add-ons to remove.'

Signed-off-by: Stephen Cuka <stephen@firemypi.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>