Move the close button into the modals

[marcoambrosini]

The close buttons should be visible within the modal windows.
cc @jancborchardt & @nimishavijay

proposed alternative (note that the close button is hovered there):

[jancborchardt]

Yes, absolutely. :) This comes up very often as an issue.
We only need to make sure that this works with the existing modals if they have content in them, like e.g. Talk group creation, firstrunwizard or password confirmation, etc.

[marcoambrosini]

How about making it a non required prop for the time being then so it's not a breaking change and we can use it right away?