Remove power_mod; Allow items to replace powers on the action bar

If an item has the line:

    replace_power=1,2

Then any instance of power 1 will be replaced with power 2 in the action
bar. Also it is possible to use:

    meta_power=true

for power definitions. The meta_power variable makes it so that a power
can't be cast (meaning it should be replaced with an item).
Make power replacement via items recursive

Also, remove an unsued parameter in PowerManager::playSound()
Regenerates the translation templates and updated the Galician (gl) translation
Remove unused code for partial background rendering

Once upon a time we had an 'optimisation' to render the background
only when needed.

There was still some cruft left, which is removed in this commit.

Fixes #1135
Merge pull request #1136 from stefanbeller/master

Remove unused code for partial background rendering
Merge pull request #1138 from dorkster/fixes

Properly handle merge stacks in equipment inventory
Merge pull request #1132 from Gallaecio/gl

Regenerates the translation templates and updated the Galician (gl) tran...
Add dev-mode command line flag
Add key for developer menu to InputState
Use C++ vectors for WidgetListBox; make list box contents dynamic
Fix typo for MenuExit.h #ifdef
Move PowerManager::targetNeighbor to MapCollision::get_random_neighbor
Add MenuDevHUD
Refactor MenuLog code into WidgetLog

Now, WidgetLog can be used elsewhere, like MenuDevConsole.
Add MenuDevConsole
Don't force a 20-char restriction on WidgetInput

Allows strings of any length, with an optional limit.
Check campaign status before unset console command
Add teleport as dev console command
Only construct dev menus if DEV_MODE is on
Fix prevent_spam behavior for logs