Fixes

• Fix installation and delete issues on windows systems (#15, #16)

• install new packages dialog with output log
• many bug fixes and style improvement

Fixed (#5) problem with displaying spinner during removal.

Added command to refresh packages list from command which can be executed from any JuyterLab plugin. Store packages list for current notebook in the StateDB, so it can be used by other plugins.

Added prefix __mljar to Python functions used to manage packages.

Improved speed by adding kernel to packages list cache.