This is quick guide how to get rid of title bars in Plasma 5. You will require mouse or touchpad with middle-click function.

*System Settings -> Application Style -> Window Decorations
Click one of the themes context menu icon
Window Specific Overrides -> Add
Click "Hide window title bar"
Use .\* for the regular expression to match all windows*

Now little tweak:

*System Settings -> Application Style -> Window Decorations
There is border size at the bottom, change it to small*

But how to maximize/minimize/restore window?

*Navigate: System Settings -> Window Management -> Window Behavior
For Window Content, Title Bar and Border set:
Modifier Key to Meta (as Alt will conflict with most of apps: viewtopic.php?f=83&t=139423 )
Left click to Move
Middle Click to Resize
Right Click to Minimize
Wheel to Maximize/restore*