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, as they are all based on `bolt/master` and should *not* be interdependent, 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!