Trilium-py

add function to add TODO item and check/unchek TODO

Improvements in attribute handling:
* nicer UI behavior for adding new attributes (new rows are added automatically) with validation for empty and duplicate names (29, 30)
* autocomplete for names and values (31)
* attributes are visible in "status bar" without opening attributes dialog (28)
* query language for attributes (26)
* removed CTRL-SHIFT-LEFT and CTRL-SHIFT-RIGHT keyboard shortcuts because they conflict with standard keyboard actions (25)

Implement basic functions of current ETAPI.

* electron icon fix
* fixed clean install (generating new DB)

* added code mirror to allow creating "code" notes (for code snippets and scripting)
* ability to execute JS code - on app startup, on request, as included in rendered HTML page
* ability to execute JS code on the backend with tailored friendly API
* refactored whole DB schema to follow camelCase for columns
* many other changes

This is first release of 0.5, previous 0.5.0 and 0.5.1 had broken electron builds.