Compatibility with android-maven-plugin-4

Since version 4.0.0 the android-maven-plugin uses the gradle / Android
Studio folder layout. This means AndroidManifest.xml is at
src/main/AndroidManifest.xml, res is at src/main/res and assets is at
src/main/assets by default. We already support non-ADT folder layout by
using Eclipse resource links to point to the actual resource. The only
thing this commit is changing that we are now reading default values
from the android-maven-plugin parameters, so we can link to the default
structure even if the user do not explicitely define these properties.

https://github.com/rgladwell/m2e-android/issues/266
Handle link changes with custom res and co.

If the project uses custom Android-related files (assets, res and
AndroidManifest.xml) and those are already linked to the custom
locations, and a later Maven update should link to the default ADT
locations, the links still remained incorrectly.

This commit solves that issue by always removing the links first.
Fix ProjectImporter destination

The ProjectImporter used the source folder as the destination to "copy"
to project into. This commit fixes that so now the project is indeed
copied into the workspace folder.
Refactor ProjectImporter

Since we only need the name of the destination project folder, the
withProjectFolder method now accepts a String instead of a File.
Test for removing links with ADT locations