Support brew on osx rather than bootstrap
Unfortunately I cannot replace bootstrap with brew on osx and guarantee reproducible production builds the way Bootstrap does by vendoring specific dependencies and versions bound to change control. However, I could make it simpler to test and develop on osx by using brew. It is anyway at this time also unclear whether I would ever deliver such production builds for macosx for sipwitches, or maybe even instead create a brew for sipwitches itself at some point in the future.
As a side note we probably do not have that deep a level of reproducible builds elsewhere anyway except on debian and the bsd's, and so that may never be an essential goal for osx. My other question to consider would be whether brew libraries would get into the application bundle thru macdeployqt, and whether I want that or not.