resized canvas to get images at bigger dimension
removed unnecessary checkSavePreview... method; exporting will be done differently
high res image export for brain and eeg visualiser
added export functionality for connectivity visualiser
implemented export images for jit drawn canvas in connectivity
export only the currently viewed canvas in connectivity visualiser
code refactoring; removed some unneeded methods and modified canvas initialisation
export figures from MPLH5 canvases; also removed not needed mimetype for image export;
fixed small png vs jpg image exporting bug
refactored mplh5 export to make resizing imperceptible
refactored gl canvas figure exporting