aerc: Add configuration to replace neomutt usage

Starting to replace neomutt in my workflow with aerc:
it is a little more lightweight, directly supports notmuch directories
and has a relatively sane configuration style (mostly just ini-like)
with 'go-templating' baked in.

In general, the configuration just feels less 'cobbled-together' than
before. I can make changes without worrying what other things are going
to break by doing so. I understand the complete configuration and
styling, instead of mostly relying on other people's formatting lines
for the styles.

I am still learning some of the configuration possibilities but it
already functions as a neomutt replacement.

office/.config/aerc/stylesets/simple

@@ -0,0 +1,14 @@
+# vim: ft=dosini
+#
+# aerc default styleset
+#
+# This styleset uses the terminal defaults as its base, by not setting anything.
+# For more details see the 'default' styleset in aerc, or the
+# aerc-stylesets(7) manpage.
+
+[user]
+attention.fg = 1
+accent.fg = 4
+highlight.fg = 3
+subdued.fg = 2
+subdued.dim = true