Fix ProjectImporter with default destination directory

If the destination directory is not set, the ProjectImporter will use
the artifact name as the project folder. But there was a problem with
calculating the destination in that case: relative path used instead of
absolute path.
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.

Related to #266.