Merge pull request #104 from codenvy/IDEX-497

Add possibility to add widget to the tab.
Don't allow null for useSSL and verifyServerCertificate properties
Fix execution button in launch bar #91
Create a messages i18n interface for "Edit datasources" - #21
Create view for "edit datasources" - #21
Create presenter and presenter factory for "edit datasources" - #21
Bind the edit datasource view and presenter factory - #21
Create action for "edit datasource" menu - #21
Show Edit datasources menu text - #21
Add "edit datasource" menu item - #21
Add dialog title to "edit datasource" - #21
Edit datasources dialog box styling - #21
The datasource manager is iterable - #21
Maintain a ListDataProvider for the datasource list in the edit dialog - #21
Bind the dataProvider and the datasource list widget - #21
(Edit datasources dialog) Add a label with the datasource list - #21
(Edit datasources dialog) Set the delegate in the view - #21
(Edit datasource dialog) add ui handlers to buttons - #21
(Edit datasources) Add delegate actions for edit and delete - #21
Bind an instance of datasourcesKeyProvider - #21