fly_monitor update: separate manual control script (control with altitude) and manual direct script (control directly the gas)

- send 0 for non detection or bad detection (under the threshold) (when in the middle =0.5 in the x axis)
- send negative to go left (when <0.5 in the x axis)
- send positive to go right (when >0.5 in the x axis)

update fly_monitor to add a test version for manual command (removed the arming part), it will the control command to the drone but the drone will not answer.

Moved unit test script to a "example" folder to avoid confusion with "navigation" folder which is the actual implementation
Update readmes

Added a new script tracking for object tracking, it allows to learn object visually (associated with focus points) and send control commands to track the object on the horizontal axis (left/right)
Removed navigation .net
Added instead 2 new .net file for each different visual control, one for the optical flow (flot) and one for object tracking (tracking)

Update view_cell script to have faster processing, it does no longer recalculate values for difference of gaussians for each image but stock those values during initalization (the beginning takes ~1 min)
Update cam_usb.hwc to the right size of the image captured by the FOXEER camera
some small update on .gcd, .sh script ...

Updated drone script to send joystick inputs to the shared memory, and added a checkbox for visual control (on vmotors)
Added a new commands script to save experiments

Changed f_out "v_motors"'s channel name to "simulation" because it was confusing with (pixhawk.control)

+ small update on fly_monitor

Added a new script : object tracking. Part of it reuses view_cells, it allows learning of view cells and associates to an object.

Added a new script for view cell based on visual place cells script by Aminata Barry https://git.cyu.fr/promethe2/multimodal_pc

Added a new altitude measure in drone script but we can't use the new and the old one at the same time for now.
In order to revert back to the old altitude, just change to link between 'alt_2_offset' and 'throttle_err' to 'alt' and 'throttle_err' in the script drone.symb.
Note: since altitude_2 is relative to mean sea level and is from the barometer (drift and big variance), some tweaks are done to make it relative to our current starting point (checkbox start_alt) and filtered (mean value).

Add a new project that combine different promethe scripts (using themis): it reuses cam_f_out, drone_joyRemote and drone_flot (with some differences)