Add requirements.txt

[NiklasKK]

Added a "requirements.txt" file for easyier "pip install installation" .
To install all required pyton modules just run "pip install -r requirements.txt"

[jonaseberle]

This is what I am successfully using with current master:

It is very similar, just allows a newer Rtree and Pillow up to the version with the breaking changes and raise numpy slightly because 1.21.0 gave me problems in DEM.smoothen():

certifi==2021.5.30
chardet==4.0.0
idna==2.10
numpy==1.21.6
Pillow<9.0.0
pyproj==3.1.0
requests==2.25.1
Rtree==1.0.1
Shapely==1.7.1
urllib3==1.26.6

EDIT: raised numpy

Let me cross-reference some topics where we talked about package versions:

https://forums.x-plane.org/index.php?/forums/topic/287422-attributeerror-module-numpy-has-no-attribute-float-error-message-mac/

https://forums.x-plane.org/index.php?/forums/topic/288397-ortho4xp-in-linux/

https://forums.x-plane.org/index.php?/forums/topic/202308-ortho4xp-mac-install-for-dummies-v130-high-sierra/#comments

[jonaseberle]

For Python 3.11:

certifi==2021.5.30
chardet==4.0.0
idna==2.5
numpy==1.23.2
Pillow<9.0.0
pyproj==3.1.0
requests==2.25.1
Rtree==1.0.1
Shapely==1.7.1
urllib3==1.26.6

(raised idna and numpy)