Ensure compatiblity with launchpadlib 1.9.7

[Leonard Richardson]

This bug is to track any changes that need to be made to this package
to make it compatible with launchpadlib 1.9.7, the version of
launchpadlib currently in Natty. Forgive the formal tone; I'm filing a
lot of these bugs at once.

In late February, I performed an audit of this project's code and
spoke on IRC with the project maintainer, so this should not be a huge
surprise. If Natty already contains a compatible version of your
package, just mark this bug "Fix Released".

If you have any questions, feel free to respond in this bug. For a
guide to the changes in Natty's launchpadlib, see this mailing list
message:

https://lists.launchpad.net/launchpad-users/msg06239.html

Quickly stores per-application credentials in a file. This does not technically need to be fixed right away, but it means that Quickly users won't get the benefit of desktop-wide integration. Here's the advice I gave didrocks on IRC:

basically we have moved to a system of desktop-wide integration instead of per-app integration
so, you don't need to store credentials in a file anymore--they'll be stored in the gnome keyring or equivalent, and they'll be shared across apps
you can stilll use the credentials file if it's present, for the convenience of your existing users
it'll look like this:
Launchpad.login_with(_("Quickly"), SERVICE_ROOT, launchpadlib_dir=lp_cache_dir, credentials_file=lp_cred_file)
if the credentials file is not present, i recommend using this code:
Launchpad.login_with(_("Quickly"), SERVICE_ROOT, launchpadlib_dir=lp_cache_dir)
so, basically, set lp_cred_file to None if the file doesn't exist
you'll get this behavior:
1. if the credentials file already exists, it will be used
2. if the credentials file does not exist, but there's a desktop-wide credential in the keyring, that credential will be used
3. if the credentials file does not exist, and there is no desktop-wide credential in the keyring, the end-user will get a browser open and be asked to authorize a desktop-wide credential, similar to how it works now

Quickly also uses the deprecated constants EDGE_SERVICE_ROOT and 'edge'; I suggest you use the string 'production' instead. This doesn't need to be fixed right away either, but it will give your users deprecation warnings.