[HTTPS-Everywhere] Minor Changes to Labels in Github

[Kate Chapman]

Hi All,

I made some minor changes to labels in Github. I did some analysis of
the current label usage and added a few additional based on experience
from other projects. This was done as part of Sumana and my engagement
announced in November(1). The two labels I'd like to highlight are "good
first issue" if there are a tasks good for a new contributor it would be
great  to add this label. Also the tag "EFF" I added this for things
that require action from someone at EFF. For the rest of the changes
please read below.

-Kate

(1)
https://lists.eff.org/pipermail/https-everywhere/2017-November/002756.html

Labels deleted (weren't in use):

* ruleset: doesn't seem necessary since there are already other more
specific labels
* Good Programmer Task: Not currently in use could use 'good first
issue' instead

Labels added:

* good first issue
* low priority
* EFF: someone at EFF needs to do this

Renamed:

* Ruleset Testing to ruleset-testing to follow the other ruleset labels
* High Priority to high priority to follow lowercase of over labels