Omegapy

* `omega_data` :
* **Full Python 3 implementation** (no longer requires the use of IDL backend routines)
* Add `my` attribute in the `OMEGAdata` class
* Allow user to apply or not corrections on channel V or L during the reading of the binaries

* `omega_plots` :
* Add usage of masks in all the dislay functions
* Add possibility to choose the longitude range between [0, 360] and [-180, 180] with `negatives_longitudes`
* Possibility to extract and replot picked spectra from interactive plots
* Function `show_ibd_v2()` renamed to `show_data_v2()`

* Add multiprocessing option for the thermal correction (`npool` parameter)
* Improve the axis limits and zoom for `show_omega_list_v2()`
* Add Save & Restore functions for composite maps

* Add the following attributes to the `OMEGAdata` class :
- `sensor_temp_c`
- `saturation_c`
- `saturation_vis`
- `summation`
- `bits_per_data`
- `data_quality`
- `target`
* Add getters for OMEGAdata lists :
- `omegapy.omega_data.get_ls(omega_list)`
- `omegapy.omega_data.get_names(omega_list)`

* Add `loct` attribute to the `OMEGAdata` class : the array of local time for each pixel as a float between 0 and 24.
* Improve the observation display : possibility to add a grid and display a high-level map (e.g. IBD) for interactive use.
* Some variables and functions dedicated to internal use were switch to private (e.g. `omega_py_path` -> `_omega_py_path`).