Rename redux selectors for menu states using "get-"

[rschamp]

In #3303 we started using selectors for project loading state, which follows the same pattern as the menus use to determine their open states. I found it confusing when first encountering the loading state selectors as "nouns" and suggested making them verbs ("get"). We should be consistent, so update the pre-existing selectors, accountMenuOpen, fileMenuOpen, editMenuOpen, editMenuOpen, editMenuOpen to use get prefixes.