Allows specifying sellable or buyable, instead of single exchangeable

* Right now you can mine towards all "exchangeable" currencies, but this presents a problem with currencies that we want to be able to sell, but not necessarily payout in. To fix this we split the config value in two.
Adds Rubycoin to defaults
Reworks the validate_address endpoint

* Validate address now allows saying which type of address you want to check against
* Frontend updated to request correct address types in correct situation
A few missed refactor areas
Fixes split payout to populate only 'buyable' currencies
Renames view variables to match
Quick hack to get JS message generation working properly again
Closes #143
Fixes JS blur action to work when changing split currency
Remove unmineable currencies from the user settings 'unexchangeable' list
Short term solution implemented for #126
Merge branch 'more_granular_exchangeable'