Update README and misc CIAtah methods

[bahanonu]

• README - update to include pain imaging book chapter information.
• initializeObj - Ensure all save paths (pics, data, log, settings, video, etc.) use absolute CIAtah private directory to match CIAtah default properties initialization and to avoid instances where users have non-CIAtah root path working directory.
• downloadCnmfGithubRepositories - Download CVX from a custom URL since the main URL sometimes has a long response time, leading to timeouts.
• modelExtractSignalsFromMovie - matlab.desktop.editor.openDocument no longer uses pwd since options.settingsPrivateSaveFolder is based on an absolute path.
• modelSaveMatchObjBtwnTrials - Remove user selecting folder to save structure to and add additional instructions.

[bahanonu]

Addresses, in part, https://github.com/bahanonu/ciatah/issues/105.

[bahanonu]

Tested in MATLAB 2020b, merging.