Reorganize client side code

[jetelain]

JavaScript code becomes more and more complex, some cleanup is being required.

The architecture of code have also to be reviewed to :

• Allow simple addition of a family of markers
• Allow simple addition of an external layer source (to allow Follow in real time on a map freindly units (Arma 3 data) #8, or After Action Report)

Switching to TypeScript would be also nice.