Fixed background colors when using dark themes

Projectlayer processing a zip of bmp files

The projectlayer file dialog now accepts files with the extension
*.3dlp.zip and will extract the contents to a temporary folder. It then
finds any *.bmp files and adds them as a set of layers.

Notes:
- Offset works, but currently scale does not affect the bmp files.
- *.3dlp.zip was chosen to mark the file as being for dlp based
resin printers, but also processable by regular archive programs.
- Have also introduced a checkbox to let the user decide to display
  fullscreen or not, as they may want the window dragged to a second
  output.

DO not clear sent lines dict after each ok - fix for firmware sending resend after ok triggering keyerror

Slicer-agnostic wording

initial hack to accept Slic3r SVG

Fix print button, add tooltips, add icons to layer preview

Ignore "wait" messages from spammy firmwares and show timestamps with received messages (courtesy of juri_)

Use system default for the background color of plater/compose function.

Update stlview.py   Double-click on window attempted to load a potentially non-existant stl file. Now prints the location and window name.

Closes #174 - Correct layer-count when z is lifted for travel moves