Change most images to be language-neutral

[GoogleCodeExporter]

Branch name:
language_agnostic_imagery

This is the repository:
https://bitbucket.org/Wuzzy2/hedgewars-wuzzy/

Branch can be viewed here:
https://bitbucket.org/Wuzzy2/hedgewars-wuzzy/commits/branch/language_agnostic_im
agery

Purpose of code changes on this branch:
Some images in Hedgewars contain English text; since images can't be 
translated, the texts they contain stay in English regardless of language.

Specically, those images were changed:
* Ammo icon for extra damage
* Ammo icon for extra time
* Loading screen image
* Preview image for portal mission
* Many campaign preview images

Here you can take a look of the changed images:
https://bitbucket.org/Wuzzy2/hedgewars-wuzzy/commits/5a9dde74127ef210296ea231117
8dc4b11ed47a8

Notably, these images are not changed:
* Trainings.png (menu button for training missons), because of a lack of a 
better idea and because of my lack of drawing skills :D
* Censored.png (shows text "CENSORED", used for seduction) → this image could 
probably be removed entirely, the effect would still work (pixelated hog) (but 
I don't know how to remove a sprite without breaking things)

Original issue reported on code.google.com by almikes@aol.com on 8 Aug 2015 at 10:08

[GoogleCodeExporter]

Whoops, I posted the wrong commit, this is the correct one:
https://bitbucket.org/Wuzzy2/hedgewars-wuzzy/commits/17931f7173fc55d3e5bb8c91006
7e0f930b2a815

Original comment by almikes@aol.com on 9 Aug 2015 at 12:31