Change default directory from "KeyStore" to something more unique e.g. "MTMKeyStore"

[Flowdalic]

Issue #24 demonstrates that using "KeyStore" as app directory for MTM may not be the wisest choice. It should be renamed to something more unique to avoid collisions, e.g. "MTMKeyStore".

MTM should ensure that if an directory "KeyStore" already exists, then this is continued to use as key store directory. If not, ie. no "KeyStore" directory has been created yet, then the new default directory name should be used and such a directory be created.

[ge0rg]

I agree with the principal idea, however there is another aspect to it.

We need to also consider the situation when the app overrides the MTM key store directory name. I'll have a look into the logic when I have some more time.