Mindtagger (tagr) presets with mixins and persistency

- tagr is now able to write tags to files and read them back later.
- Preset is a set of predefined tags (specified by a tags schema) and supporting custom UI elements (item rendering and tag rendering).
- Multiple presets can be passed over the command-line, and in such cases we mixin templates to support a wide variety of combinatorial scenarios without having to write custom code for every case.
For example, if one has to judge the precision of predictions over items with NLP parse info, then by choosing two presets "precision" and "nlp-tags", one can get the words related to the predicted entity highlighted and custom controls for quickly tagging each item as correct or incorrect, while the words in each sentence are rendered with side info, such as NER, POS tags.