UIforETW with WPA Preview support, etc.

This release of UIforETW defaults to tracing-to-file, looks for WPA in the path to support the preview version of WPA in the store (!!!), ensures that all scripts work with Python 3, and various other fixes.

The full list of changes can be found with:
git log --oneline 70bbcaa..c0b5b79

A partial list includes:

3aa62e6 Remove python27 hack
cf87c3f Find wpa.exe in the path to support store versions
4e4854b Update build scripts to Python 3 and add logging
e10e0e7 Make VirtualFreeStacks.py more helpful
04d4ed1 Python 3 and style-guide fixes for StripChromeSymbols.py
937323d Python 3 fix for ETWPackSymbols.py
a4d392a Improve error handling for CPUByCommandLine.py
5d5e97e Update xperf_to_collapsedstacks.py to Python 3
7e4bca1 Experimental JavaScript tracing support
1fd1327 Add /a to signtool invocation
9d7d94f Merge pull request #149 from FireDaemon/issues/#118
a544b69 Load registry value string only of type REG_SZ
b0990e5 Add handle tracing batch file
653d384 Change default to Tracing to File
6e9ad6d Add VirtualFree stack summarizing script
04c7ba7 Used a GUID-named mutex to find whether UIforETW is running
d7c1d9e New version of RetrieveSymbols.exe
25f1764 Clarify confusing GUID-length message
e5c4345 Mention DISK_IO omission when circular buffer tracing

The etwpackage*.zip file contains 32-bit and 64-bit versions of UIforETW.exe, statically linked so that they will run anywhere. No compilation required. It also includes 64-bit versions of the Windows Performance Toolkit (WPT) installers.

To use this release just download etwpackage*.zip, unzip it, then run bin\UIforETW.exe (signed). WPT 10 will be installed as needed. Symbols are available on this symbol server: https://randomascii-symbols.commondatastorage.googleapis.com

For more information see https://tinyurl.com/etwcentral (aka https://randomascii.wordpress.com/2015/09/24/etw-central/)