Do not inject maven dependecies by default and make this part a configurable mojo

[laeubi]

Currently we inject the dependencies computed by Tycho into the maven model for two cases:

1. To allow Maven to sort projects properly
2. To allow other tools to discover them (e.g. dependency:tree)

For the first part, we would technically only need reactor projects, and even this is not strictly required when Tycho extends the GraphBuilder. For the second, there is always a problem with some cases it works, in others it creates trouble and in some it is even useless work that slows down the build.

Because of this, this part of Tycho should become an own mojo, so different aspects can be configured where the default should be:

1. Only inject reactor projects
2. Do not resolve p2 > maven coordinates

Other use-cases (e.g map p2 > maven, inject all or only given scopes, ...) can then be configured by the user with the usual maven configuration in the configuration pom.