Added suspend/resume of Model.update_plot()

If changing several parameters at once, the plot would currently update
once for each change. This commit adds a suspend_update() /
resume_update() function pair to temporariliy disable updating until all
changes have been completed.
Disconnect/reconnect parameters on suspend/resume

Disconnect parameters to update_plot on suspend_update, reconnects on
resume_update (if _get_auto_update_plot() returns True). Also changes
_get_auto_update_plot() to check for suspension, as several internal
functions rely on it. Because of this, it is important that
resume_update decrements the counter before it checks
_get_auto_update_plot.
Docstring updates Model.suspend/resume_update
Merge remote-tracking branch 'tomas/BUGFIX_EELSmodel_weights' into 0.7.1
removed MARKER_* outside class, proper init for marker
Automatic style corrections courtesy of autopep8
created metadata, moved marker to metadata
Automatic style corrections courtesy of autopep8
Fixes #282: wrong energy scale when reading FEI ser files.
Merge pull request #283 from francisco-dlp/BUG_FIX_FEI_energy_scale

Bug fix fei energy scale
move some functions out of classes
Automatic style corrections courtesy of autopep8
bugfix with metadata marker
added run_count to metadata
Automatic style corrections courtesy of autopep8
changed to fail_count, as only that makes sense to record
Automatic style corrections courtesy of autopep8
parameter_domains initial
Automatic style corrections courtesy of autopep8
something broken, just a checkpoint