Activate Network mode at all times

[dondi]

The Network Mode switch should permeate more of the app, controlling any functions that will differ based on whether GRNs and PPIs are involved:

• menu item should be available when GRNsight first loads
• then it would affect which file types are allowed in the Open File menu and which default network type comes up in the Load from Database modal.
• When “Load from Database” is chosen, the Network Type dropdown can default to whatever the currently-selected Network Mode is from the main UI

[dondi]

The second bullet in the description may need discussion alongside #1066 request to have the opened file determine the network mode

[dondi]

Upon discussion, we can go ahead and eliminate the second bullet from scope in favor of #1066 but we will still enable the Network Mode dropdown for informational purposes—switching it even when there is no network open should enable/disable other corresponding options based on network type