Add page on running Scratch locally

[Samq64]

Resolves #542

Todo:

• Linking different component branches to scratch-editor and scratch-www
• /session with working login
• Maybe find an alternative for Redirector because it is MV2

[Samq64]

@mxmou How have you been logging in on localhost? The only way I have found that works is creating a network override and manually copying the contents of Scratch's response over which is not ideal.

[mxmou]

@mxmou How have you been logging in on localhost? The only way I have found that works is creating a network override and manually copying the contents of Scratch's response over which is not ideal.

I set the target of the /session redirect to a data URI containing a valid response. This way, I can also test new Scratcher accounts, membership, etc. by changing the appropriate flags in the response.