Resolve "migrate to python 3.7"
- migration to python 3.7
- requires web2py 2.18.3 or above
- require matplotlib 3.1.1 or above
- require pandas 0.25.2 or above
- migrate to update tool to build application (w2pext/utilitites version 1)
- Move plugin documentation to docs/plugin_dbui
- Remove the obsolet callback IS_IN_USET
- New mechanism to initialize plugin_dbui
- Imporve LoaderException.js to improve error reporting
- Closes #33 (closed)