First step of completion refactoring.
Extraction and move of variable completion related classes.
Adding visibility filter - structure view is able to filter non-public functions/variables

Closes #72
Quite a big refactoring + referencing namespace prefixes for all places but xml + referencing to predeclared namespaces. Unified namespace referencing.
Merge pull request #82 from arnostv/visibility_filter2

Adding visibility filter
Folding of functions, namespace declarations and imports

Closes #50 - Folding of functions
Closes #23 - Imports and namespaces declarations folding
Closes #64 - Add parameter info tooltip.
Merge pull request #83 from arnostv/folding

Folding of functions, namespace declarations and imports
Fix formatting for xpath step expressions.
Move test data to correct package.
Fix edge case for folding.
Fix indentation for function body started with comment.
Get rid of warning.
Restructuring test sources.
Restructuring test sources.
Rename tests to make patterns simpler.
Small refactoring of function completion.
Tests for parameter info tooltip.
Issue #32 - Built-in function completion.
Issue #32 - Built-in function completion - add parameter info handling.