The `neoVimBuffer` function was updated in qvacua#1015 to used a lua script
through `nvimExecLua`. The script returns the dictionary retrieved from
the `getbufinfo` vim functions. The issue is that this can grow very
large, especially the `variables` entry, and can cause the lua stack to
grow too big and error.

In the end the `neoVimBuffer` function only needs a small handful of the
entries from `getbufinfo`, and so the lua script has been updated to
return a dictionary with only those entries.

At the same time the `hasDirtyBuffers` function was found to also return
the `getbufinfo` dictionary and was similarly fixed. It was also noticed
that the argument passed into `getbuinfo` here was a vim style
dictionary and not valid lua. This made `hasDirtyBuffers` fail and
caused an issue in `MainWindow.windowShouldClose` where selecting `File
> Close Window` would close the window even when dirty buffers were
present. The proper lua dictionary syntax is now used and fixes this
issues.

Fixes qvacua#1044