(base) Added hooks that can be used by controllers to take actions at the appropriate time during an action

Changed base class from ApiControllerBase to ApiMutableModelControllerBase
Fixed incorrect string concatenation (+ instead of .) in getNodes()
Removed stray parentheses
Extracted static fields for gridFields and gridDefaultSort

o Recovery console is weird, just use CTRL-C from anywhere
o Simplify the early installer invoke by probing for keypress
o Display a brief message when installer+SSH is active

Prefer LiveCD boot during install media boot, then
set up an extra user for installation.  This user
shall be reached via console or SSH soon enough for
a sort of remote install experience.

PR: https://forum.opnsense.org/index.php?topic=3403

Inspired by: DragonFlyBSD (and we're using its installer anyway!)

This reverts commit 6c6b861e.

(mvc) merge ApiModelControllerBase and ApiMutableModelControllerBase + define class statics properly. as discussed at https://github.com/opnsense/core/pull/1124

PPPoE wasn't removed, which led to some refactoring to find
out why.  The outcome is the same, but works a little bit
different now.  While there, make it possible to omit the
config write in case we are going to call write_config()
shortly after anyway.

This will also be necessary for the legacy VPN plugins.

PR: https://forum.opnsense.org/index.php?topic=3480.0

(firewall, scrub) add direction and source port. closes https://github.com/opnsense/core/issues/1087

Incorrect units capitalization in proxy form

(packet capture) stream/flush output to browser, closes https://github.com/opnsense/core/issues/1116