GUI browse URL improvements

[hjoliver]

A user reminded me that browsing suite and task URLs from the GUI does not work if (a) the GUI is not running on the suite host account; and (b) the GUI account does not have non-interactive ssh access to the suite host account. Reason: the GUI simply invokes the cylc doc / cylc browse command, which parses the suite definition - which can't be done from a remote account with no non-interactive ssh access to the suite host account.

Main change in this PR:

• store suite and task URLs in the daemon state summary, for use by the GUI

Also:

• allow use of string templates to replace suite and task names in URLs (was our old-style pseudo environment variable syntax, retained as well for back-compatibility)
• tidy some associated GUI code a little
• User Guide: document exact requirements for remote access to suite-parsing and file-retrieval commands, including via the GUI; and clarify the same for suite client commands

[hjoliver]

@matthewrmshin - in light of recent emails - I should add to the documentation on this PR, about the effect of a shared filesystem between GUI host and suite daemon host. My new section on the GUI and ssh is for the non-shared case.

[matthewrmshin]

In the future, we should modify the GUI so that all relevant commands are accessed though the API of the running suite (with the exception for suites running on $USER@localhost?) so we don't have to rely on non-interactive SSH.

[hjoliver]

Yes and no - some of the current GUI functionality could not easily be done that way, e.g. edit the suite definition! (But we could decide that's not what the GUI is for, I guess). The other concern is, do we want huge suite or job logs being served up by the suite daemon?

[matthewrmshin]

Not easy, but possible. Imagine a work flow like this:

• GUI downloads the content of the suite.rc from suite.
• GUI starts an editor for the content.
• On change, GUI uploads the content of the file to the suite.
• Suite runs reload with the uploaded content.

On large files, I am not sure what the impact would be on the suite, but I would imagine that it is no different from how Rose Bush serves log files via cherrypy.

[hjoliver]

Fair enough, it certainly is possible. For the future web GUI, we should either do that or drop these functions of the current GUI.

[hjoliver]

Still TO DO: #2449 (comment)

[matthewrmshin]

Looks OK in general. Worth adding some doc strings to new and modified methods in cylc.gui.app_gcylc.

[hjoliver]

Updated docs for the shared filesystem case, added some doc strings, and rebased to master. Hopefully this is good to go now.