Electron microscopy translator suite

[ramav87]

Currently, we have a mix of translators that are rather poor for electron microscopy files. Need to create a suite of new translators to clean up the problem. Specific classes will be developed for each of the following

1. Nion (single images are in ndata, multidimensional goes to h5, otherwise).
2. Digital Micrograph
3. FEI
4. EMD (Berkeley)

At some point, SEM should also be incorporated, along with atom probe tomography. A lot of these functions are available in pyTemlib (https://github.com/gduscher/pyTEMlib/blob/master/pyTEMlib/dm3lib_v1_0b.py and https://github.com/gduscher/pyTEMlib/blob/master/pyTEMlib/file_tools.py )