Allow creating new files without a workspace

[vince-fugnitto]

Expected Behaviour

As a user, I'd like the ability to create new files without a workspace or folder necessarily opened.
This will allow for a wider scale or use-cases for end-users who might want to edit files temporarily, use Theia as a scratchpad, or even do single-file editing such as a python script or markdown file.

Actual Behaviour

Theia does not currently support creating files without an explicit workspace opened which limits itself from more use cases by end-users.

Implementation Proposal

Allow files to be created regardless if a workspace is present or not.

• Create untitled files which can be saved in a temporary location by Theia until they are explicitly saved by end-users.
• Enable the menu option / command New File when no workspace is present (currently disabled)