steam-api: refactored internal account ID storage
steam-api: error upon low poll timeouts

After a period of time, poll requests will begin to timeout after one
second, rather than the set timeout value. This leads to a great deal
of HTTP spam which is completely unwarranted. While the exact cause is
unknown, it is probably related to the relogon when the current Steam
API session expires.

A check for this error must be implemented to prevent excessive HTTP
requests. Moreover, even after the root cause has been determined, and
the issue has been resolved, it should be ensured the timeout is not
too low.
steam: Fixed setting `show_playing` during account runtime

The plugin is suppose to revalidate the buddy list of an account that is
online when `show_playing` is changed. Currently, the plugin neglects to
do this correctly, and the buddy list is not revalidated at all.

Additionally, any invalid user mode should disable the feature. While
this worked, a check was added to ensure an invalid mode was not set.