Simplified locks

For easier use by organizations coming from the (now deprecated) locks-and-latches plugin.

Main Jenkins config:
![jenkins-config](https://cloud.githubusercontent.com/assets/5141243/3906452/0d0e0110-22f3-11e4-826c-07d2c5264521.png)

Individual job config:
![job-config](https://cloud.githubusercontent.com/assets/5141243/3906454/11708ec6-22f3-11e4-8013-2d573ab9d1de.PNG)