updated Eclipse setup instructions
include Apache Commons IO for easy reading of the AES encrypted binary file
ensure OtrAndroidKeyManagerImpl is created whenever getInstance() is called

Instead of passing in the central keystory File in one place, and a null in
another, pass in the Context in both places, and move the filename into
getInstance() since that's the only place that ever needs it.  Otherwise if
the OtrAndroidKeyManagerImpl instance does not exist yet, and the arg is
null, getInstance() returns _instance which is still null.
add WRITE_EXTERNAL_STORAGE so Gibberbot can delete imported file from sdcard

With the AES file import mechanism, once the file is imported, Gibberbot
should delete it to signify that the import has completed successfully. To
do this, it needs the WRITE_EXTERNAL_STORAGE permission.
add AES-256-CBC encrypted file importing for OtrAndroidKeyManagerImpl