Write mmcif header

[jamesmkrieger]

Now we can add a full mmCIF header to a new set of coordinates, e.g.

In [1]: from prody import *

In [2]: ag1, header1 = parseMMCIF('D_1292146224_model-review_P1.cif', header=True)
@> 30156 atoms and 1 coordinate set(s) were parsed in 6.96s.

In [3]: ag2 = parsePDB('refined-coot-3.pdb')
@> 29673 atoms and 1 coordinate set(s) were parsed in 0.29s.

In [4]: writeMMCIF('D_1292146224_model-review_P1_chimera-coot-6-refmac-coot-3-prody.cif', ag2, header=header1)

[jamesmkrieger]

Actually, this isn't quite there

[jamesmkrieger]

This now more or less works but it is very very slow. It also doesn't have anything about the order of non-loop tables and the starDict that I've made is not a useful structure for interrogating the metadata.

I'll probably improve it further to address these 3 points

[AnthonyBogetti]

@anupam-banerjee Also can you check this one too?