transmit/receive modes for each of downlink and uplink frequencies

Here is my proposal for issue #336 (closed)

Notes :

• The mode field on the transmitter (transmitterEntry) model has been renamed to downlink_mode
• I added a uplink_mode field on the same model
• During the migration that add the new uplink mode field, this field is initialized with the value of downlink_mode (old mode field) if the type of transmitter is different from transmitter (so in other words, if there is a uplink frequency) and also if invert is true and the downlink_mode is USB, then the value of uplink_mode will be LSB and vice versa. I don't know if invert applies on other modes than SSB, i don't think so, but let me know :) .
• Quid of the invert field after that ?
• The modals (edition, creation and administration) had been updated

Here are some few screenshots of the results :

UI :

API :

PS : The mixed uplink and downlink modes are randomly made for testing, it's not based on real cases :)