fixing "Using a DataArray object to construct a variable is ambiguous, please extract the data using the .data property" issue introduced in xarray 0.19.0

fix "outside area" error occurring when making a flow map with XRSite (which fails because local wind at (0,0) is requested

add selfsimilarity blokage model
prepare for gradients
New structure. Old WakeModel mainly in new EngineeringWindFarmModel
add deflectionmodel
update documentation

- add missing h_i parameter in call from calculate_AEP
- update parqueFicticio grd files
- change site.probability function to take ws_bins instead of ws_bin_size
- correct probability calculation in WaspGridSite
- add test that compare WaspGridSite with results from Wasp (raw data, u_mean, air_power and aep)
- add function in OneTypeWindTurbines to instantiate from tabular data

- example: noj_terrain_following.py
- move all distance calculation to distance.py
- old TerrainFollowingDistance function(from Movflot) renamed to TerrainFollowingDistance2
- new simpler and more efficient TerrainFollowingDistance implemented
- WaspGridSite renamed to WaspGridSiteBase.
- New backward-compatible WaspGridSite that allows different Distance calculation objects
- tests

deleted test_examples.py as all example modules are tested in test_main.py

- ti_map added
- default ti changed from 0.75 to 0.075

Merge branch 'update_uniform' of https://gitlab.windenergy.dtu.dk/TOPFARM/PyWake into update_uniform