Remove dependency on MsBuild Community Tasks

[dazinator]

Currently depend on this package to provide msbuild tasks for creating zip files etc.
However it get's dragged into peoples solution when they add DnnPackager NuGet Package (because we currently need it) and it pollutes the solution by adding a .build folder and all sorts. This can be scary for people, and I also don't like it.

With #15 we are implementing all of our build / packaging logic in Unit testable, C# build task classes, including the zipping logic. This hopefully means we can get rid of MsBuild Community Tasks as a dependency.

[dazinator]

This will be closed when I merge from latest dev branch.