rewrite dialect input with exec() statements.

[stefanfluck]

Currently, each new dialect requires 1) a dialect.py file in the dicts folder and 2) a couple of lines in the make_static routine. automate that with exec('command as string'). Therefore, any kind of string can be supplied in the namelist, and just the file can be supplied in the dicts folder.

alternative: make path of dicts folder/file also an input in the namelist. if none provided -> use current path as it is now.

[stefanfluck]

use mpd = importlib.import_module('palmpy.staticcreation.dictfolder.'+dialectvar')