Add HMI brightness entity

[sveinse]

Adds support for setting the status light brightness.

Fixes #112

[sveinse]

@c0mplex1 this PR will introduce a new line translation-line. See the commit. What is the Dutch translation for the same line? I can update the PR with the Dutch translation as well.

[c0mplex1]

"hmi_brightness": { "name": "Helderheid statusindicator" }

Please change the following to a better Dutch translation ... or can/may I do this myself?

"installation_type": { "name": "Installatie type" },
"max_current": { "name": "Maximale stroom" },
"installation_type": { "name": "Installatie type" },
"max_current": { "name": "Max stroom per fase" },

"operating_mode": {
"name": "Operatie-modus",
"operating_mode": {
"name": "Opladermodus",

"deauthorize_and_stop": { "name": "Deautoriseer het laden"},
"restart_charger": { "name": "Herstart de oplader" },
"deauthorize_and_stop": { "name": "Deautoriseer het laden"},
"restart_charger": { "name": "Herstart het laadstation" },

[c0mplex1]

I have made the changes in my "own" fork.
Do I need to create a new pull request?

[sveinse]

@c0mplex1 if there are more translations than just setting the HMI brightness translation, I'd prefer it in a separate PR please.