Merge branch 'develop'

Merge branch 'drop-pagedata' into develop

Replace type Pagedata with plain string

Merge branch 'api-improve' into develop

Remove unused funtion Orientation.toString()

Introduce a constant for the "trash" ID

Use a dedicated type for event types

Provide a function to set up a default client

Move message to separate file

Make internal api models private

Merge branch 'layers' into develop

Place document and drawing on separate layers

Reduce opacity for highlighter

(.git)Ignore .bak files

Add link to remarkable wiki in README