Make faction open command async as everything there is thread safe. Resolves issues of players timing out servers in. Closes #84

Refactor scoreboard usage

In preparation for team colors, we need to unify scoreboard usage into a
single scoreboard per player.

Rather than creating a new scoreboard for each desired sidebar
objective, we provide an interface FSidebarProvider that allows
implementation-agnostic retrieval of the title and lines of the desired
sidebar, along with appropriate methods in the new implementation of
FScoreboard.

The new FScoreboard implementation manages the currently-visible
sidebar, with methods to set default (non-timed, with update interval)
and temporary (timed, no update interval) sidebars.

Temporary sidebars are replaced with the default sidebar upon
expiration.
Refactor scoreboard issue. Resolves issue #80.
Support modded enums in gson using custom EnumTypeAdapter. Resolves carbon breaking materials in issue #90.
Add /f seechunk command for visualizing a chunk
Merge branch '1.6.x' of https://github.com/drtshock/factions into 1.6.x