Keep transaction in profile

Requires: !514 (merged)

Closes #319 (closed)

Partly covers: #294 (warning appears if user tries to modify signed transaction or refresh it's metadata)

In this MR:

• transaction is added to storage and being kept with rest of crucial data
• transaction summary no longer loose signatures when leaving screen (after loading signed transaction from file)
• added refresh metadata feature (available only if node is online)
• ConfirmActionDialog is appearing user tries to refresh metadata or modify loaded (signed) transaction in transaction summary screen
• added warning with information that signatures of transaction were invalidated when user adds an operation to previously loaded (signed) transaction from file
• fixed case when loaded transaction (with signature) was saved with signed checkbox and error occured