Bug fixes and tweaks (pre-alpha.0.6.1)

This update contains a few fixes and tweaks.

• Damage range values for enemies are now stored in the enemy type data instead of hard coded values, so different types of enemies can now deal different amounts of damage.
• The item information popup that is shown when right clicking an item now also displays the item's image.
• Added hover effect to item slots in the inventory.
• The player can no longer move around while the inventory screen is open.
• Fixed regressed bug that caused items to disappear when attempting to put it into an incompatible equipment slot.
• The encumbrance amount should now update correctly when moving items around in the inventory and when merging stacks of items.
• Fixed combat music volume becoming messed up when quickly activating combat mode multiple times in quick succession.
• Fixed combat movement being choppy when moving by holding down both mouse buttons.
• Equipping items on a party member should no longer cause their portrait to be toggled open.