Co-Authored-By: StephenSmith25 <56431339+StephenSmith25@users.noreply.github.com>

Needed to add checks around makedirs(), throws an error if the directory
already exists.

If the table was repopulated at any time, any plotted workspaces would
be added to the plot every time the table was updated. Resulting in
extra lines shown on the legend that couldn't be seen on the plot.

Should have fixed these as I went along, but I'm not sure where they
failed to fixup the commits. Most were introduced as a result of
handling the checking of the plot box when repopulating the table.

Observer pattern uses has the data widget as an observable that sends
the plotting widget the workspaces to add or remove from the plot when
the 3rd column in the table is ticked and unticked respectively. The
pattern also handles the removal of indiviual workspaces or the
clearing of all tracked workspaces.

Co-Authored-By: PhilColebrooke <52415735+PhilColebrooke@users.noreply.github.com>

Python 2 has a different method of sorting its dictionaries, so the
comparisons were failing after iterating through them.

Makes the loading process use run numbers if they are available. Falling
back to using the filename to collect data and finally using the
workspace name as is.
Also changes the finder to encourage the use of nexus files.