Add powerline initialization plugin

Initializes powerline per the official powerline documentation:
https://powerline.readthedocs.io/en/master/usage/shell-prompts.html#bash-prompt

plugins/available/powerline.plugin.bash

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+
+cite about-plugin
+about-plugin 'enables powerline daemon'
+
+command -v powerline-daemon &>/dev/null || return
+powerline-daemon -q
+POWERLINE_BASH_CONTINUATION=1
+POWERLINE_BASH_SELECT=1
+bashPowerlineInit=$(python -c \
+	"import os; \
+	import powerline;\
+	print(os.path.join(os.path.dirname(\
+	powerline.__file__),\
+	'bindings', \
+	'bash', \
+	'powerline.sh'))")
+[ -e $bashPowerlineInit ] || return 
+. $bashPowerlineInit