sbt: add postgres driver
Abstract: set some text size limits

- set text length limit on model to 2500
- set text length limit in editor to 2000
- set acknowledgements limit in editor to 200
- set other text input limits in editor to 100
Serializer: fix bug with disappearing author mail

- 'mail' was serialized as 'email'
editor: figures can now be deleted
editor: better state handling

- withdrawn abstracts can be reactivated
- check state and state change before save
- remove hover edit buttons in non editable states
editor: some texts changed
msg.js: view model base class for messages
editor.js: prepare for MessageVM integration
editor.js: MessageVM integration done
Merge pull request #110 from stoewer/master

Editor bug fixes and messaging view model

LGTM