Correct PalasoUIWindowsForms.Tests.csproj to have 2-space tabs

Visual Studio generates this file with 2-space tabs, so that is
what we need to have in the repo.  Additionally, before this
change, the indentation was a mix of tabs and spaces.
Merge pull request #121 from andrew-polk/master

Correct PalasoUIWindowsForms.Tests.csproj to have 2-space tabs