Adding support for multiple windows

[tlund101]

This PR relates to #5601 and fixes a regression (reported in #5761 ) caused by #5377
Work is being tracked internally by INS-2235 as well.

I've tested deep links on mac and they still work fine. I'm unable to test CLI arguments on Mac, as it always attempts to open a second instance, instead of hitting the second-instance event of Electron. Another thing I wasn't able to test is changing titles of different windows.

There may be more esoteric features of Insomnia I didn't test, but the basic collection creation and request functionality seems to work. Editing two things at the same time isn't supported, but also doesn't cause any errors. For example, editing an environment will save the environment that is closed/edited last.

Unfortunately in my second commit I had to remove the accelerator for a new window, since it would also send Cmd+N (creating a new request) at the same time it created a new window. I suspect this is a current issue in the release branch, though, if you change hotkeys to match accelerators.

[jackkav]

thanks for the contribution, I picked this up and completed it over here #6104
should be in the next release