Support analysis of source-containing root projects

[autonomousapps]

This plugin currently assumes that, if it is applied to the root project, the only possible relevant classpath is the buildscript classpath. However, it is possible and quite common for (generally simple, uni-modular) projects to have source in the root. An example is the Dependency Analysis Plugin.

[handstandsam]

Re-opening, wrong issue! Meant #2 .

[art-shen]

It's an important request.

It would be very helpful for simple one-module projects or test projects. Currently, it is always necessary to create unnecessary submodules.

[art-shen]

@handstandsam I can make a PR request for this if you would consider such a change.

[einarpehrson]

@handstandsam I can also volunteer for this.