several refactoring steps

DEL: removed several redundant methods

MOD:
- changed GUI-field name for sino-directory to be consistent (and
added a plug so that it can still be loaded from old config-files)
- switched off edge-padding by default in singleSliceFunc, to be
consistent with default pipeline value
changed class name of AdvancedChecks to better reflect its purpose
outsourced all GUI-dialogs to "ui_dialogs.py"

DEL: obsolete properties from "DatasetFolder" class
MOD: templates to incorporate changed GUI-field name