UI improvements.
Merge pull request #17 from l1ll1/CVLFAB-545-two-part-ui

Cvlfab 545 two part ui
Added menu item for displaying HTML Help
Added "see also" links to SSH Keys and SSH Agent Forwarding
help pages.
Ensured that pressing return/enter will automatically run OK
button's event handler.
UI improvements
UI improvements
Adding to repository.
Merge branch 'CVLFAB-545-two-part-ui' of https://github.com/CVL-dev/cvl-fabric-launcher into CVLFAB-545-two-part-ui
Change key passphrase dialog now seems to work as intended on Linux
and Mac OS X (using pexpect).  Still need to do Windows implementation.
Moved SSH key dialogs into a subdirectory.
Updated import module names.
Now using sshKeyDist.sshpaths to determine location of SSH binaries.
Because I'm testing scripts from the command-line (not building with
PyInstaller etc.), I'm using a dodgy method to find the sshKeyDist
module in the parent directory (adding it to sys.path) for now.

DeleteKey module now uses a class.

Fixed a bug where InspectKey could display a non-Launcher fingerprint
from the agent, instead of the Launcher fingerprint.
Porting to Windows (which doesn't like pexpect).
Dialog now hides irrelevant fields, depending on radio button selection.
spelling
Fixed typo
Change passphrase dialog now uses a separate PrivateKeyModel class
to change the passphrase.

Deleting a private key now also deletes the corresponding (local)
public key file if it exists.
Change passphrase dialog now uses a separate PrivateKeyModel class to
change the passphrase.

DeleteKey now deletes the (local) public key file as well as the
private key file if it exists.
Removed PrivateKey.py, which has been replaced by PrivateKeyModel.py