Fixed package validation.

 #KT-5352 Fixed
Package and units validation fixed.
Check if unit exists by OS methods, not by eclipse resources.
New Kotlin project wizard GUI created.

 #KT-5377 In Progress
New unit wizard page class refactoring.

Minor: name conventions
Default Kotlin perspective for all wizards.
SelectionListeners replaced with SelectionAdapters.
Refactoring: setErrorFormMessage -> validate.
Default project name is empty string.
Copyright added to NewProjectWizard.
AbstractWizardPage created, NewProjectWizardPage now extends the abstract one.
Constant strings refactoring.
Colon autoadding to label text.
GridData autocreating for controls.
Separator static factory method added.
Added method that checks creating object exists.
NewUnitWizardPage refactored and now extends AbstractWizardPage.
Operations refactored.

Minor: name conventions
Now NewUnitWizardPage doesn't show error messages on start-up.
Only public classes can only be imported by quickfix.

 #KT-5360 To be discussed