New visualizeQFeatures function

[leopoldguyot]

• add dimension reduction box in the summary tab of processQFeatures
• refactor pca_box (should contain parameter widgets)
• Refactor summary_tab to separate the processQFeatures global logic from it
• Add an across set intensity visualisation (for one high level feature, inspect the intensity of all the feature levels linked to it (in a selection of sets))
• Bundle the summary tab (without the download button) in a standalone visualizeQFeatures app

[leopoldguyot]

• MIT -> GPL-3