Tip modifier interface imported from peer4commit

Project owners can now choose the amount donated to each commit.

They have a new button "Change project settings" on the project page along the project name.
In this screen they can change 2 things (for now):
* a text describing their tipping policies that will be displayed on the project page on peer4commit
* a checkbox that will put all new tips on hold when commits are found

When the checkbox is active, each new commits generates an "undecided" tip and the authors are not notified.
The project owners can then click on a new button on the project page to decide the tip amounts. They have these choices:
* Leave undecided (to decide later)
* Free (the commit won't get any tip and the author won't be notified)
* Tiny: 0.1% of the project balance
* Small: 0.5% of the project balance
* Normal: 1%
* Big: 2%
* Huge: 5%

The authors are notified when the tip amount is decided (unless they have recently been notified already, or if they said they don't want any more notification, or if they have configured their peercoin address).

The 2 buttons are only available to project collaborators (those who can push changes to the supported repository).

See also previous discussions: tip4commit#70 and sigmike/peer4commit#44