Incorporate triaxiality into main code

[shenmingfu]

This is a list of things we want to do. We will make individual issues for them.
The triaxiality code is in https://github.com/LSSTDESC/CLMM/tree/issue/591/triaxiality/examples/triaxiality

1. Put data_functions.py into dataops

• functions to rotate coordinates and shear assuming we know orientation of halo's major-axis
• functions to calculate theta and radial bins for lensed sources
• functions to calculate from data DeltaSigma_const, DeltaSigma_4theta, DeltaSigma_constX, DeltaSigma_4thetaX

2. Put model_functions.py into theory, for example func_layer.py

• function to calculate monopole component of gamma_T with and without ellipticity 2nd order correction term
• function to calculate quadrupole term of g_T
• functions to calculate from model DeltaSigma_const, DeltaSigma_4theta, DeltaSigma_constX, DeltaSigma_4thetaX, and DeltaSigma_monopole

3. Stacking the data of different clusters for triaxiality analysis (this is a long term goal; may need some resampling methods to estimate error bars, e.g. demo_mock_ensemble )
4. Create jupyter notebook demonstrating a use-case with mock lensing sample.

Other tools:

1. Coordinate rotation: rotate the model/data using the cluster's angle
2. Get the angle of the cluster (currently assuming it's known, so used as an input)