Added Open/Save/Zoom-to-Fit to Mission Editor

Restored ability to load and save missions from / to files while offline from vehicle.

![screenshot_2014-07-08-11-03-46](https://cloud.githubusercontent.com/assets/4014433/3511639/7e38d332-06b1-11e4-8907-67ca545f7b2f.png)

![screenshot_2014-07-08-11-06-02](https://cloud.githubusercontent.com/assets/4014433/3511660/aa995f1e-06b1-11e4-8baa-b0e071e0edc7.png)