Fix start up race condition

It is possible for the application designer documents to be already open
when the DocumentMonitorService is created.  If so we will miss the show
methods for the IVsWindowFrame instances.  This change fixes that by
scanning for already open IVsWindowFrame instances on creation.
Startup settings now associated with project

Previously the startup debugger settings were stored in the .csproj.user
file.  This meant that a new clone of SaveAllTheTime or branch switch
would eliminate the start up / debugging settings for the project.  By
putting them into the .csproj directly we eliminate this problem.

Additionally this uses the $(DevEnvDir) variable instead of hard coding
the directory to Visual Studio directory.  This makes the setting
tolerant to x86 versions of Windows as well as non-traditional install
locations (some people like to install Visual Studio on the D drive).