Adding support for block finder bonus

* Added new configuration option `block_bonus`, see `global.inc.dist.php`, default 0
* Added new transaction types: `Bonus` and `Orphan_Bonus`
* Changes transaction table structure, added upgrade SQL
* Changed findblock cron to credit bonus to finder
* Modified transactions class to reflect changes

Fixes #148
Merge pull request #153 from TheSerapher/issue-148

Adding support for block finder bonus

Fixes #148