feat(workspace): bootstrap internal work space

This commit adds internal workspace bootstrapping once the user opens up
the modeler for the first time.

The location of the workspace is
 {user.home}/.camundaModeler/workspace (linux/unix/mac)
and
 {appdata}/camundaModeler/workspace (windows)

As initial workspace contents, a skeleton workspace in
{modeler.home}/workspace may be shipped that acts as a blue print.

Closes #13
chore(workspace): move skeleton workspace
feat(installer): add windows installer

This commit adds an installer generator script to the modeler that
creates windows installers via NSIS.

Closes #10
chore(installer): ignore generated executables