Add ability to run history scripts

[cbrnr]

In some situations, using a GUI is just slower than typing a command, for example when renaming a bunch of channels according to a specific scheme. In such cases, the ability to enter Python commands would be very useful.

[cbrnr]

Maybe running arbitrary Python code is too complex and dangerous, but we could add an option to run a previously saved history script. This would mean that a subset of Python commands would work (basically everything that MNELAB can generate).