Transformed plugins to be usable as plain Maven plugins.

[NiklasRentzCAU]

This involves a few changes:

• All KLighD plugins are still built as Eclipse-Plugins to be usable in P2 Update sites
• All plugins are recognized in Eclipse as Maven artifacts to allow the dependency handling to consider Maven-related dependencies
• added binding to language server to avoid an error in derived language servers, stemming from a newer Xtext 2.28 release. Fixes Erroneous language server injector configuration with Xtext 2.28 #144.
• In the .lsp artifact: replace swt, eclipse.ui and jface dependencies by a mock implementation providing the interface for KLighD's internals but no functionality (as that is not needed in the language server case). Allows to build a platform-independent LS.
• In the klighd plugin: added two separate poms for launching with the SWT mock from Eclipse. The main one will build correctly with plain Maven using the SWT mock dependencies, but launched from Eclipse it would still use the real SWT dependencies from the P2 target platform, the alternative pom.xml forces Eclipse to use SWT (but should not be used in a Maven build).
• configure to not publish interim pom artifacts such as repository, target platform, and features
• reorganize parent pom artifact of all plugins to be the main build parent to avoid needing to publish the interim plugins pom.xml that does not contribute anything.
• removed specific piccolo offscreen renderers from klighd.standalone. These offscreen renderers can instead by registered by simply including the corresponding piccolo artifact as a dependency, then it will be automatically registered via service loader. This requires applications to use the offscreen renderer to explicitly list piccolo as a dependency now.

This change will allow to release Maven artifacts and therefore fix #78. This change will make it not necessary anymore to completely remove all SWT and alike dependencies from KLighD, invalidating #63. Closes #63.

Other:

• removed Batik feature and plugins from the build process. Fixes Remove batik #109 and Remove batik #134
• there is no guarantee yet that all artifacts on their own have the correct Maven dependencies to be fully working as intended, mainly the LSP is in focus here. Missing dependencies may be added later.

Yet TODO:

• Add configuration and further information for publishing the artifacts to Maven Central via Sonatype.
• First release the dependencies on Maven Central to make this build work (SWT Mock, KLighD.Piccolo2D)

See kieler/KLighD.Piccolo2d#1