Added VideoResource to the sewi.resource module
Corrected static method definition
Added missing import for the Concept model
Corrected missing self references for properties
Adjusted VideoResource to adapt to Concept restrictions

VideoResource will now detect resource datatype via the concept mimetype field, and its mimetype via the value_text field.
Added private constants
Added a basic logging statement
is_video_concept is no longer a private method
Fixed is_video_concept() failing to work with static constants
VideoResource now refers to its site location as 'url'
Fixed video UUIDs not being recognized as proper IDs in the URL
Fixed video data not being serialized properly
VideoResourceViewer will now load the video data from the backend
Defined helper functions for resource unit tests
Added VideoResource test setup code
Added test for VideoResource initialization
VideoResource now reads mimetype from the associated Concept properly
Added test to ensure VideoResource data integrity
Number of database calls for VideoResource reduced