Add central team storage and team browser

[marksg07]

This feature would be super cool to have from a user perspective. It solves two issues that have often annoyed me, and (I'm guessing) many other users:

1. Using PS on multiple devices. I play PS on my home desktop computer, my work laptop, and my phone at different times during the day. When I play, I often will make modifications to my teams. When I want to switch to a different device, I have to export my team to pokepastes or email it to myself from the original device, and then get the team and import it on the other device. This is a pain in the ass to do multiple times per day.

2. Sharing teams with other people. There isn't a central repository of teams that I can look through if I want to try using a new team. Also, if I want to share a team with a specific person on PS, I have to export to pokepastes and message them either through PS, which I believe only works if they are online, or through some other medium, which (again) is a pain in the ass. And in order to use someone else's team that they have shared with me or the world, I have to grab their team export and import it into my teambuilder.

Both of these issues could be solved by maintaining a central team database on a PS server that could be directly accessed through the client. Essentially, users could upload teams to this database publicly or privately -- publicly would mean that the team could be found by anyone through a public team browser; privately would mean that only certain users could see the team (by default, just the person who uploaded the team). This solves the first issue, because I can upload my changed team privately before I switch device, and then download it from my "uploaded teams" screen on my new device. As for the second issue, I could share my team with someone else using their PS username (even if they were offline), and they could download that team from their "shared teams" screen. There would also be a "public teams" screen. All of these lists of teams could be searchable by team name, user name, and possibly even pokemon or pokemon sets.

(Duplicated issue? See smogon/pokemon-showdown#815.)