Alternate Search Modes

While working on rotoCap today I thought a nice feature would be allowing the user to manually launch rotoCap on a per-frame basis instead of a run of the whole image sequence. Additionally I am adding a flag to the keying sub-process whether or not to overwrite existing keyframes on a drone. If existing keyframes are found then the engine can use them as initial search coordinates, saving time by not having to start at the origin of a UV plane during the initial UV survey.