Play item sounds in MenuVendor

This plays sounds when items are returned/added to either of the vendor
tabs.
Remove cppcheck-warnings from sound manager and harmonize coding style.

[src/SoundManager.cpp:59]: (style) The scope of the variable 'psnd' can be reduced.
[src/SoundManager.cpp:42]: (warning) Member variable 'Sound::chunk' is not initialized in the constructor.
[src/SoundManager.cpp:152]: (performance) Prefer prefix ++/-- operators for non-primitive types.
Merge pull request #361 from stefanbeller/master

Remove cppcheck-warnings from sound manager and harmonize coding style.
Merge pull request #358 from dorkster/bugfixes

Play item sounds in MenuVendor
Added game_prefix in engine/misc.txt for ability to segregate saved games
and stash for different games/mods.

Removed duplicated code for stash loading.
Merge pull request #363 from hean01/master

Remove of hardcoded sound effect references in MenuManager
Merge pull request #366 from hean01/game_prefix

Added game_prefix in engine/misc.txt for ability to segregate saved games
Fix broken MenuConfirm instances in GameState menus

Changes reflect recent modificatons to menus/menus.txt formatting.
Merge pull request #370 from dorkster/bugfixes

Fix broken MenuConfirm instances in GameState menus