- Moved backend determination to `config.el`
- Replaced unnecessary backquote construct with simple quotation
- Replaced `pcase` form with only one-arm with `when` or `unless` form
Add new packages `mvn` and `maven-test-mode`.
Move `gradle-mode` configuration from groovy layer to java layer
New prefix commands `SPC m m` for maven and `SPC m l` for gradle.
Make maven and gradle commands available in java-mode.
Update documentation.