Survos 1.5.0 release

[OllyK]

SuRVoS 1.5.0 includes a number of changes:

• the ability to save classifiers and then then reload them and apply them to new data
• the ability to add extra training data to a reloaded classifier and retrain it
• Fixes for axis label bugs in the 'label splitter' perspective
• Up to 10 undo (Ctrl z) and redo (Ctrl + shift + z) slots when annotating
• Minor bug fixes related to Python3 and MRC file export