Initial Xtext-based setup and grammar definition for Metaflow

This is an Xtext-based implementation of the Metaflow language from
the Culturegraph project. For now, it's basically a port of the
Metaflow ANTLR3 grammar to Xtext, providing an Eclipse-based editor
for Metaflow *.flow files.

To create and run the editor in an Eclipse instance with Xtext 2.3
installed, open the Metatext.xtext grammar file an choose 'Run As'
-> 'Generate Xtext artifacts'. Then, choose the org.lobid.metatext
project, 'Run As' -> 'Eclipse application'.

In the launched workbench, set up a project and copy or create some
Metaflow *.flow files. They will open in the generated editor,
which provides basic syntax coloring, auto completion, and outline.
Fix redundant directory structure
Set up and integrate a Maven/Tycho build for the Metatext projects
Add a p2 repository to install the Metatext editor in Eclipse

After a `mvn clean install` you can install the editor into an
Eclipse instance from the local p2 archive: in Eclipse, choose
'Help' -> 'Install New Software' -> 'Add...' -> 'Archive...' and
select the 'org.lobid.metatext.p2.zip' file from the 'target'
directory of the 'org.lobid.metatext.p2' project.
Basic launcher setup to run *.flow files in Eclipse

Allows files edited with the *.flow editor to be launched directly
in Eclipse (select a *.flow file -> 'Run' -> 'Run As' -> 'Metatext
Workflow'). The current implementation has several limitations:

- Metaflow dependency was created with a patched 'pom.xml' for
`mvn clean assembly:assembly` in metaflow (jar-with-dependencies)
and added to metatext as a jar dependency
- With the metaflow dependency, the language infrastructure can't
be generated in metatext (remove dependency temporarily to
re-generate artifacts)
- The 'metaflow-pipe.properties' file was created and added to the
jar manually (otherwise it is overwritten by the most recent file
with the same name from any project in the metaflow dependencies)
- Paths in the flow file (input, morph definitions, etc.) need to
use absolute paths (the absolute path can be extracted to a var
though)
- Output from flow files to "stdout" is not visible inside Eclipse
(it's printed to the console from which Eclipse was started, if
"-consolelog" is passed)
Update dependency to include N-Triple encoder support in Metaflow
Tweak release script (wipe old p2 repo, create directory listings)
Set up xtend-maven-plugin for clean Metatext build
Update release script for new p2 repo location
Tweak build settings for Travis (more output, use Travis mirror)
Add initial Metatext usage documentation
Remove Metatext from parent pom, build both in .travis.yml
Run complete metatext build (install w/ tests) after lodmill builds

The separate `mvn test` causes an issue with the xtend-maven-plugin
Tweak settings.xml to fix mirror issue in Travis build
Generate products (Windows, Linux, Mac) during the Metatext build

After a build (`mvn clean install` in metatext/), product zips and
folders can be found in org.lobid.metatext.p2/target/products/.
Add upload of product zips to release script
Log errors during flow execution, can be seen in the error log view
Resolve references to the current directory ('.') in *.flow files

The default Metaflow support for portable *.flow files does not
work when running in an Eclipse plugin on a workspace file
('current' directory when running is not where the input file is).

This commit adds support for portable *.flow files with direct
execution in Eclipse. When running a *.flow file in the workspace,
read its content and replace '.' references with the absolute path
to the workspace location containing the *.flow file to run. Write
the new content to a temp file and pass that temp file to Metaflow.
Open error dialog with root cause of exception during Metaflow run
Generate lodmill-rd jar-with-dependencies as part of the build

- Generate jar with mavn assembly:assembly
- Copy correct properties files into jar
- Copy jar into the org.lobid.metatext project
- Add generated jar to .gitignore
- Integrate jar deployment into Travis build
- Only release in release.sh, don't build