[processing] improve help system

[alexbruy]

Description

Adopt Processing to use QgsHelp class and improve algorithm dialog usability:

• "Help" tab replaced with "Help" button which opens algorithm documentation in the default webbrowser (consistent with other QGIS dialogs)
• short help widget now resizable and can be collapsed. Useful for power users. State of the widget (collapsed or not) remembered and restored between sessions.
• short help widget has "collapse" button to hide/show it in one click.

Checklist

Reviewing is a process done by project maintainers, mostly on a volunteer basis. We try to keep the overhead as small as possible and appreciate if you help us to do so by completing the following items. Feel free to ask in a comment if you have troubles with any of them.

• Commit messages are descriptive and explain the rationale for changes
• Commits which fix bugs include fixes #11111 in the commit message next to the description
• Commits which add new features are tagged with [FEATURE] in the commit message
• Commits which change the UI or existing user workflows are tagged with [needs-docs] in the commit message and containt sufficient information in the commit message to be documented
• I have read the QGIS Coding Standards and this PR complies with them
• This PR passes all existing unit tests (test results will be reported by travis-ci after opening this PR)
• New unit tests have been added for core changes
• I have run the scripts/prepare-commit.sh script before each commit

[rduivenvoorde]

Nice work Alex!

[DelazJ]

I like the "collapse" button idea. Could be handy for the Expression Builder dialog...

[elpaso]

Nice! But shouldn't the black triangle collapse control be at the top instead of the bottom?

[pcav]

Great, thank you Alex.

[alexbruy]

But shouldn't the black triangle collapse control be at the top instead of the bottom?

I have no strong opinion about this. Collapse button was placed at the bottom because at the top there is a "Run as batch" button and having two button so close looks a bit overloaded for me. Also it is easy to misclick. But if having collapse at the top is better I will move it.

[alexbruy]

Collapse button now moved to the top.

[pcav]

Just tested, in my case clicking on Help apparently does nothing. Anything special I should do?

[DelazJ]

@pcav I suppose this help button will be effective once Matteo and Alexander grant proposal is implemented

[alexbruy]

Just tested, in my case clicking on Help apparently does nothing

This is expected. Processing algorithms are not documented and documentation for master is not ready.

[pcav]

Thanks for clarifying. Looking forward for the new stuff to test.

[pcav]

What happens to the minihelp already available?

[ghtmtt]

if I add the following path to Settings -> Options -> System -> Documentation paths:

http://docs.qgis.org/2.99/en/docs/user_manual

and then test the Help button with a QGIS core algorithm (e.g. multipart to singlepart) the link then the browser looks for the following (not existing) link:

http://docs.qgis.org/testing/en/docs/user_manual/processing_algs/qgis/qgis:multiparttosingleparts

instead of the right one:

http://docs.qgis.org/testing/en/docs/user_manual/processing_algs/qgis/vector_geometry_tools.html#multipart-to-singleparts