enable symbols as custom block label parts

as well as enabling Costumes to become Symbols, and additional symbols
(speech bubble, arrows, robot)
Symbol selection menu for BlockLabelFragmentMorphs
Merge pull request #219 from MMSequeira/master

Correct Portuguese translation of 'When I receive' hat block.
Portuguese translation update
enable Symbols in InputField drop down menus
enable Symbols in InputSlotDialog Morph’s drop down menu
filter quotation marks from project names

(for backend index)
only show symbol menu for label fragments

in InputSlotDialog
customizable drop-down menus for input slots

still experimental and incomplete and therefore commented out
(inactive) for now
cloud project saving transmission integrity check

includes the sizes of the sent project components in the transmision,
so the cloud backend can check if the whole of them have been
transmitted before comitting to the database
Improve translation of 'stop script'.
Improve translation of clone creation text.
Merge with upstream.