If the user manually toggled on (or off) the main menu sidebar, automatically remember and restore that state on next page load / startup

[nekohayo]

In v5 (tested on the Pro SaaS version), if you toggle off the main menu's sidebar with the < button, close the browser (or the tab) and reopen the page, its state gets reset open on the next load. Also, it gets shown in situations where it isn't realistic to show it.

• If not pinned to a particular state It should also probably auto-collapse when space is clearly insufficient, which would help a little bit with my "small dedicated tasks list / time tracker window" usecase.
• If the user explicitly opened or closed it, then it should automatically remember its user-set state, per device with a browser cookie (i.e. I want it to be always closed on my tiny window app mode, but not on my full-width big browser, which are two different browsers).

To be usable in closed state, its icons should have alt text and title hover labels: invoiceninja/ui#1355.