Remove optional dependencies from composer.json

[tobiastom]

As discussed in #112 all optional dependencies should be removed that are not required to run PHPCI.

When a plugin misses a dependency it should complain about it (maybe some general missingRequirement() method that every plugin could call if it misses something).

• [x] Move optional dependencies into suggest section
• [ ] Add some general way for plugins to complain about missing dependencies

[meadsteve]

One option might be to move them in to suggest in composer.json:

{
    "suggest": {

    }
}

might make it a bit easier for someone who knew they wanted to use a lot of the plugins and useful from a reference point of view so we have an idea what things have been developed against.

[tobiastom]

+1

[dancryer]

+1 also.