Update AssemblyInfo.cs files.

-Update the AssemblyInfo.cs files for JSon2Txt and ResourceGenerator to
match the metadata in Microsoft.DotMet.Build.Tasks (e.g. the copyright
string, company, etc.)
Update LICENSE file.
Merge branch 'update-assembly-infos'
build.cmd uses either MSBuild 12 or MSBuild 14

Previously our repositories would build in either a Dev12 or a Dev14
Developer Command Prompt, but only if Dev12 (for MSBuild 12) was
on the box due to a hard-coded path to MSBuild 12.  This change
will use MSBuild 14 if MSBuild 12 is not available.
Merge branch 'use-msbuild-12-and-14' of https://github.com/FiveTimesTheFun/buildtools
Fix build script to use default web proxy to download remote files.

Applying fix from corefx to buildtools
https://github.com/dotnet/corefx/commit/423f9ec7e322d8d22da7f006b245f9770732ba5e