2d image fitting

[Kechil]

related frontend issue CARTAvis/carta-frontend#1397

This is to provide users the ability to select a region and fit a 2D function such as 2D Gaussian to get feature properties. Note that full resolution image data need to be used as fitting input, instead of downsampled data.

Requirement document:
https://docs.google.com/document/d/1E9kL7FOhVtkDDit8VIYle61tU5PzSYXjnLpxZBCHliY/edit?usp=sharing

Implementation plan:

• Basic single/multiple gaussian fitting and text outputs
• Gaussian fitting with fixed initial values
• Gaussian fitting of the current view in frontend
  ---- target for v3b3 ----
• Output model/residual images
• Estimate progress and listen for cancellation messages
• Gaussian fitting of selected regions
• support a background level in the fitting
• support different solvers in the fitting
• also use beam deconvolved image as the input data for fitting moved to new issue Image fitting with beam deconvolved images #1236

[kswang1029]

Requirements:

• provide 2d gaussian function as a start.
• capability to define initial guess of fitting parameters (via a dialog or draw a box with cursor)
• capability to fix part of fitting parameters
• provide fitting results in convenient units (e.g., gaussian center in pixel and wcs coordinates)
• provide fitting errors
• capability to fit multiple gaussians (could consider to have an upper limit, say 3 or 5) in a single shot
• export fitting results as a text file

[Kechil]

v1.5