Add python hydrograph

Add a hydrograph that shows:

1. daily
2. monthly
3. yearly
4. seasonal

simulated and observed discharge and KGE and NSE.

TODO:

• create hydrograph
• create system to specify which plots to create
• make callable from command line
• fix problems with ticks for shared row (solution: removed monthly)
• add xlim
• add sum diff and percentage - how much is the total discharge over/underestimated
• make testable
• write tests