fix AddNodeTag() call + SHOW_FLOATING_LEGEND() uses small details as default

[kirchsth]

related to #334

• AddNodeTag() is fixed that it can be used like all other Add*Tag() calls.
• SHOW_FLOATING_LEGEND() is fixed that default size of details is small.

@startuml 

!include http://raw.githubusercontent.com/kirchsth/C4-PlantUML/extended/C4_Deployment.puml

AddNodeTag("nodeTag", $borderColor="orange", $borderThickness="3")

Boundary(b5, "Boundary 5") {
  Node(node, "Node", "Type", "Optional Description", $tags="nodeTag")
  Node(node2, "Node2", "Type", "Optional Description")
}

SHOW_FLOATING_LEGEND()
@enduml

It can be tested via my extended branch

wemu can you please test it.
(atm it looks the the online server has sometimes problems with include, if this is the case please test it with a local plantuml version)
BR Helmut