patch 1.0 of plot.py: Added a save option for skymap, skymap_* return fig by...

Patch for km3astro.plot for the implementation in the shifter tool website.

List of changes:

- Added a save option for skymap
- skymap_* return fig by default now (for shiftertool website)
- added dataframe input option in skymap_*
- added option for the User to choose the title
- changed skymap alert color to darkgreen and darkred.
- Changed path + name to os.path.join in skymap_*
- applied change to tests and examples folder.