Svg doc framenum and filenamesocket

Слиты nikitronn запросил слияние svg_doc_framenum_and_filenamesocket в master

Created by: zeffii

adds filesocket.

this exposes an incompleted feature of SvTextSocket class.

  • quick_link_to_node is not implemented/ignored, if prop_name is passed

this also brings up a new issue,

  • maybe quick_link should be allowed to pass a string reference to a post_node_placement_function, to allow the quick_link to place the added node in a specific state which is most useful to the user. right now we are at the mercy of the default state of a node.
  • maybe it's time to create an additional simple text node, like NoteNode but with SvTextSocket in/out (or user changable per socket)