Config: absolute paths in project config file

This fixes #43 by removing the file paths from the system and project config files.

For old config files it might be necessary to delete the paths manually in some cases.
Merge pull request #44 from stoewer/gndata-editor-43

Config: absolute paths in project config file
Main Window: add tabs to main panel

Fixes #46
Merge pull request #47 from mpsonntag/gndata-editor-46

Main Window: add tabs to main panel
main elements for query view
Add support for importing of metadata
RDFTreeCtrl: Handle model change events
MenuCtrl::askForFile: accept extensions filters
MenuCtrl::importMetaData: set ExtensionsFilters
query grid pane with fields add/remove first draft
small cleanup
Merge pull request #50 from asobolev/master

backbone for Query Tab

LGTM
MenuCtrl: use Opt.ofNullalbe for chooser results
MenuCtrl: askForFile takes a title param now

Make it more generic
MenuView: move "Import Metadata" to project menu

Also add trailing "..." to indicate it will open a dialog.
Merge pull request #49 from gicmo/md_import

Curde support for metadata import

LGTM
query execution in the query pane
table pane added + some refactoring
some cleanup
Merge pull request #53 from asobolev/master

First draft of query view components

LGTM