Update model editor

[tsole0]

Description

• Added GUI box for direct form volume function editing to PluginEditor.py (dd7819a, 98c0a31, 6dc2f84)
  • Auto-insert first polydisperse parameter into GUI box (b35ee1c)
  • Add tooltip and sample function to GUI box (3ea3929)
• Changed text of GUI for clarity (3ea3929)
• Updated Python model template
  • Add flags and explanatory text (b3bc16f, 5ccb501)
  • Adds Effective Radius and Volume Ratio functions to non-polydisperse model template (d28cba7)
• Added capability to generate and save C models (bb37054, 84c7bdb, 2cc5296, 8bf8960, 3c26555, 8f7f7f2)
  • Added checkboxes to plugin editor giving user option to generate Python and/or C model templates (1251c38)
  • Created template for C models containing all kernel-defined functions and instructions for use (84c7bdb, f16633f, 5ccb501)
• Linked Python and C files together by inserting source = ['filename.c'] into Python model template if both Python and C are generated (27ac6d6)
• Run model checks on C code and report errors (NOT a C syntax check, but a MODEL check via sasmodels) (0c61d51, a1d04b3)
• Added error popups for intuitive use:
  • Error if user does not specify model type (54b1159, bb61fb7)
  • Override dialog if user tries to save a model that contains errors asking if they would like to save or continue editing (20212f6, 7790233)
  • Info popup if user generates C model with no python model informing them that model checks will not be run (faefb31)
  • Warning popup if user loads a model with errors into model editor (a1d04b3)
• Parameter tables in plugin widget GUI expand to fit available space (068cdb1)

Note: Merged #2917 into branch to fix tests Note: Shares two commits with model-editor-bug-fixes branch (ba4cbc7, 26e6b59) because ba4cbc7 originated on this branch and 26e6b59 was necessary for error-checking C models

Linting: de25165, 3ea3929

How Has This Been Tested?

TODO: windows installer, mac installer

Review Checklist:

[if using the editor, use [x] in place of [ ] to check a box]

Documentation (check at least one)

• [ ] There is nothing that needs documenting
• [ ] Documentation changes are in this PR
• [ ] There is an issue open for the documentation (link?)

TODO: Need minor documentation changes!!

Installers

• [ ] There is a chance this will affect the installers, if so
  • [ ] Windows installer (GH artifact) has been tested (installed and worked)
  • [ ] MacOSX installer (GH artifact) has been tested (installed and worked)

Licencing (untick if necessary)

• [x] The introduced changes comply with SasView license (BSD 3-Clause)