Non-orthonormal basis implementation

[DarianLP]

The implementations are the following:

1. A new flag in the input file called "# Orthonormal". The two options are: true, false. For example

#Orthonormal
false

The parser_input file will read the flag and store it. If there is no Orthonormal flag, the code assumes that it is true.

2. In the file parser_wannier, if the orthonormal flag is false, it will read the overlap matrix from the _tb.dat file. The format is almost identical to a Wannier file, with the real-space overlap matrix printed at the end in the same format as the real-space Hamiltonian. If the orthonormal flag is true, as it is by default, the overlap matrix is assumed to be the identity.

3. In the file constants_math, a new subroutine called diagoz_gen is implemented, which is similar to the subroutine diagoz but now solves the generalized eigenvalue problem to take into account the overlap matrix.

4. In the file ome_sp.f90, if the orthonormal flag is false it uses the subroutine diagoz_gen to solve the vme kernel, if the orthonormal flag is true it uses the subroutine diagoz.

5. Typo in the file exciton_envelopes concerning coordinates. (credits to @mauricioquintela)