Fixed plugin location in development environment

Use user home directory to deduce plugin location
in development environment.
Use predefined scopes with IDEA

Using custom scopes in the IDEA module file is no longer working since
Gradle 1.12 (see
http://forums.gradle.org/gradle/topics/adding_configuration_to_idea_module_scope_after_upgrade_to_gradle_1_12_fails).
Replaced the custom scopes with prefined scopes instead.