GUI loading of base network connectivity from API

[gtdang]

This enhancement was discussed in #723.

The idea is to move away from setting connectivity and drive parameters from input files. Alternatively connectivity would be loaded from pre-defined options that load connectivity using the hen-core API. And drive parameters will be set by the user.

Figure 1 Current implementation

Figure 2 New implementation

The changes are summarized below:

1. On the Network Connectivity tab window:
   • A dropdown-selector for a set of pre-defined base connectivity configurations
   • A confirm button to load the selected base connectivity
   • These replace the current "Load local network connectivity" button. As users won't be loading only connectivity from file.
2. On the External Drives tab window:
   • The current "Load external drives" can be removed as users won't be loading only drives from file.
3. New "Load saved network" button
   • This button will load both connection and drives from an hdf5 file. There is no option to load just connections or drives--it will be all-in-one.
   • This gives the user the ability to save configuration state of a tutorial and return back to it. It also allows us to supply a configuration state mid-tutorial if needed.
     • Note that this does not save the state of the simulations or plots generated