cherrytree 0.11 issued

• implemented the memory of expanded/collapsed nodes, which is active when the preference option “expand all nodes when loading the tree” is not flagged (thanks Allan)
• implemented the imports from tuxcards and basket, fixed bug in the import from keepnote (thanks Tharsice, Andriy)
• implemented the opportunity to export the selected node and its subnodes as a cherrytree file (thanks Marcin)
• added the Polish language (thanks Marcin*2)