Add project description to settings editor and share dialog

[riknoll]

adds project description to the settings editor and the share dialog (this feature is behind a pxtarget.json flag).

other assorted changes:

• gets rid of the save button in the settings editor. it only affected the project name (all other fields autosaved) so i just made it so that project name also autosaves
• converts all the SUI components in the settings editor to react common components
• target contributed checkboxes in the settings editor now render as toggle switches just like our other checkboxes
• clicking "edit settings as text" now pops a warning dialog that warns you that you could ruin your project and advises that you download a copy first
• changed the color of "edit settings as text" to red so as to indicate danger
• fixes the resize property for the Textarea component
• changes "project title" in the share dialog to "project name" so as to be more consistent with our other UI