update changelog and versioning

Updated tracks rendering to completely avoid non-visible tracks to im…

…prove performance. Closes #25

Merge pull request #27 from awetomaton/design/known_sources

Design/known sources

Merge branch 'develop'

Fixed bug where an index error was thrown if the histogram was turned…

… off and VISTA was run programmatically. Fixes #17.

Fixed bug where the slider frame range for selected sensor is based o…

…n max of frames of detections and tracks across all sensors. Removed `sensors` as a programmatic argument. It is already required for the `Imagery`, `Detector` and `Track` objects. The unique sensors list is determined from these.

Improved AOI creation logic so that it creates AOI based on user's vi…

…ew rather than image extent preventing issues where users couldn't see AOIs they cerate when zoomed in.

Added median and subspace background removal algorithms for static ta…

…rgets.

Fixes #11: bug where frame slider range didn't update when changing s…

…ensor selection

Added the ability to set the user's name in the Settings dialog. Labe…

…l user name and label time is stored and saved to exported detections and tracks.