Python 3 support (#755)

* Python 3 support

* Fix import_vs_environment in xenia-build

* Drop support for Python 2

* Fix CIs and xb.bat

* Require Python3.4+ because of Ubuntu Trusty

* popen.communicate returns bytes instead of string

* Useful info in travis

* universal_newlines should be True

* Changed shebang to python 3

* Python 3 shebang fix

* Clang python 3 shebang fix

third_party/clang-format/clang-format-diff.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 #===- clang-format-diff.py - ClangFormat Diff Reformatter ----*- python -*--===#
 #

third_party/clang-format/git-clang-format

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 #===- git-clang-format - ClangFormat Git Integration ---------*- python -*--===#
 #