Added support for storing the merchant items in the database

[itzandroidtab]

This adds support for the following:

• support for buying items
• Items are regenerated after timer expires.
• Limit on the amount of times you can buy a item
• Items are stored in the database and the same items will show up after a restart
• Buying stackable items will stack them
• Buying an item will update the UI to show the new item
• Merchants get created when entering the merchant menu for the first time
• Merchants get deleted when deleting a character.
• Added mapping for merchant to stock id for correct text next to the merchant when selecting a item
• Support to buy items with money from the stash (after #175)

There is one limitation for now:

• Currently not all goblin merchant items are mapped. I only added the first one for now

Solves issues: #145 and #147