Improve behaviour and wording of plugin config "Video Portal"

[dagraf]

Is your feature request related to a problem? Please describe.
At the moment the 'default template' does not get shown when the option "Publish Series on Video Portal" gets activated when creating a series. This leads to the fact, that if you only configure one default template, the option "Publish Series on Video Portal" is empty when it gets activated during the creation of a series (see screenhsot).
In addition, the explanation in this config tab is not optimal

Describe the solution you'd like

• If only the default template is configured the option "Publish Series on Video Portal" does NOT get offered while creating and editing series.
• Wording in plugin config:
  • In the subtab "Permission Templates" change the description below the title "Permission Templates" to: "All but the default template can be chosen from when creating or editing a series. If a template gets chosen, the configured role with the given permissions and actions will be set on the series. The roles of the residual templates will be removed."
  • Change the description of the setting "Default Template" to: "This template will be used if the series should not be published to the external video portal. Therefore, only one template can be defined as the default template. This template can not be chosen when creating or editing series. Do not set a default template if you don't want to set roles and actions for series which do not get published to the video portal."

Additional context
This feature request is related to this (allready fixed) bug: #132