#36 group by subprojects

Limit number of results - show only subprojects name instead of all available commands for all subprojects until a whole project name is already typed.

For example - assuming:

root project has task aTaskInRoot
3 subprojects: :ab, :ac and:de`
each subproject has tasks: taskA, taskB

then:

./gradlew <tab>

shows:

aTaskInRoot
ab: 
ac:
de:

```
./gradlew a<tab>
```
shows:
```
aTaskInRoot
ab: 
ac:
```
```
./gradlew ab:<tab>
```
shows:
```
:ab:taskA
:ab:taskB
```

Partially solves: https://github.com/gradle/gradle-completion/issues/36

Tested on monorepo with tens of subprojects and tasks, both bash and zsh. Without that, a developer is overwhelmed with hundreds od tasks...

gradle / gradle-completion

#36 group by subprojects #86