Boot updates

Branch `boot_updates` merges all of my work from Saturday, if you'd like to accept it all as such. Feel free to pull any of them individually if not, but I figured I would save you the headache and go ahead and offer them merged as well.

I'll be closing the individual pull requests, but the relevant branches and affected topics are:

Commit | Issue | Title
---|---|---
e4a4e6f389cdd3d3bb069bb254b5b399dc953841 | #1526 | Bootstrap process can't resolve Bolt root from CLI environment
76349f15462680a0ba98731c379b1dcb9ba91b08 | #1527 | lib.php is located in app/classes/ and pollutes global scope
b6b8e3ffb79337f1d713ab334a889921f7a0b5fa | #1530 | Reduce global scope pollution during bootstrap procedure
1ee9d660eb043d96bf96ad1650dc61d9364c6584 | #1531 | Low level environment checks should be entry-point agnostic

Thanks!