Remove dependency on MongoDB

[vilcans]

MongoDB is nice and all, but it's a bit overkill for a minimalistic CI server. (IIRC, by default a MongoDB installation uses at least 3 GB of disk, which can be a problem if you want to run builds on a really cheap VPS.)

I'm proposing adding a setting for what storage to use, and add the possibility to save to the file system instead without using a database server. It could use a GDB database or be just as simple as storing everything in a JSON file.

I've done some work in this direction already, so I'm probing the interest in a pull request here.

[gabeio]

mongo at minimum uses about 300 mb of data on the disk no where near 3gb what would all that data be? it can hold up to 2gb on x32 and more on x64... but I do agree that for a minimalistic CI this is overkill.

[ryankee]

Sorry guys, I've been swallowed by client work for the last several months. So let me say this: Any and all pull requests that can be validated by more than 1 person will be merged.