Fix new box creation

This commit fixes following Errors:
- Box is not hidden when hiding directly after creation
- Created Box is appended instead of prepended in first column after refresh (position update missing)
Implement #6 - number of shown issues per box
Prevent same custom box creation

If the box with title and filter id is already present (either in all projects or in the current project) the new box is not created.
Update for v0.7.0
Bump version to 0.7.0

Changes:

- Add input to select number of shown issues to custom box dialogs.
- Bugfixes for custom box creation (displaying and preventing creation of same box)