add option to insert cell above the current cell

[ianhi]

It would be nice to be able to control if the snippet is inserted above or below the current cell. For instance, when you open a new notebook and want to paste in an import cell it would be nice to have it be the very first cell.

possible solutions

1. The extension uses the jupyterlab settings editor for this
2. use comments in the snippets to add metadata. Something like:

# <snippet-metadata>
# placement = 'above'
# </snippet-metadata>

p.s.

A++ on this extension - it's much nicer than my hacky bash + xdotool + gnome keyboard shortcuts approach