Allows characters to have equipment and wealth

This patch allows characters to have equipment through possessions and
coins through wealth.

It also displays the game system’s equipment in the equipment list when
levling up the character.

This should complete the back-end side of the equipment selection
process.
Remove Intercom
Fixes suggested by pull review
Fix psych security issue
Allows characters to buy and sell equipment

This patch ensures that characters can sell and buy equipment
correctly. At the current moment, equipment is sold at 100% of value.
This might need to be changed in the future.

This also adds a javascript Flash class, which allows something like
`new Flash(‘hello’)` to display a flash to the user.
Test Possession serializer
Test character level #to_i
Merge pull request #21 from ekampp/equipment

Fixes #9