Move Diagrams component to it's own module

[amolenaar]

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Documentation content changes

What is the current behavior?

Main window and Diagrams were in the same module. This made the module quite big (~500 lines).

What is the new behavior?

Main window and Diagrams each have their own file. This makes it easier to use them.

Does this PR introduce a breaking change?

• Yes
• No

[sourcery-ai]

Sourcery Code Quality Report (beta)

✅  Merging this PR will increase code quality in the affected files by 0.04 out of 10.

Quality metrics	Before	After	Change
Complexity	0.75	0.46	-0.29 🔵
Method Length	47.92	48.65	0.73 🔴
Quality	8.84	8.88	0.04 🔵

Other metrics	Before	After	Change
Lines	639	430	-209

Changed files	Quality Before	Quality After	Quality Change
gaphor/ui/mainwindow.py	8.83	8.90	0.07 🔵
gaphor/ui/tests/test_diagrampage.py	9.22	9.22	0.00
gaphor/ui/tests/test_handletool.py	8.73	8.73	0.00

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Overall	Recommendation
gaphor/ui/mainwindow.py	MainWindow.open	2	242.82	5.61	Split out functionality
gaphor/ui/tests/test_handletool.py	test_connect_comment_and_actor	0	250.78	5.75	Split out functionality
gaphor/ui/tests/test_handletool.py	test_iconnect	0	163.90	6.63	Split out functionality

Please see our documentation here for details on how these metrics are calculated.

We are actively working on this report - lots more documentation and extra metrics to come!

Let us know what you think of it by mentioning @sourcery-ai in a comment.

[danyeaw]

Nice idea!

[amolenaar]

Thanks 😊