Loading the hero_options file is done across mods amending to existing file

This enables custom hero portraits easily added via a mod, which just
extends the hero_options file by a line and adding a portrait.
Add an assertion to make sure we are not dividing by zero. (Found by scan-build)
Merge pull request #752 from hansjoachim/assertion

Add an assertion to make sure we are not dividing by zero.
Fix up/down being locked when MenuLog is open

Closes #751
Merge pull request #754 from dorkster/menu_log

Fix up/down being locked when MenuLog is open
Fix 753.

Thanks @hjd for finding these.

As a bonus: Formatting of AStarContainer (tabs instead of spaces)
Fix possible null pointer dereference
Merge pull request #755 from stefanbeller/fix753

Fix 753.
Merge pull request #750 from stefanbeller/customportrait

Loading the hero_options file is done across mods amendingly