many changes

a. some cleanup
b. redesign contacts list
c. private does not used in the code as string only as byte array (also
saved as a separate file in device
d. keys deleted from memory only 15 seconds spec goes to background
e. improved pull from db
f. added session status to the contact screen
g. fixed nfc problem (not able to move keys to nfc tag)
h. added notification after saving keys and close dialog.