export (all) macro(s) by popup menu

[octaeder]

This PR adds a popup menu to the Export button of the Edit Macros dialog. This allows the user to choose whether to export current or all macros.

So there is no need to know where txs stores the macros internally.

[sunderme]

the usual gui element for this kind of things is a combobox (see sections/labeles etc. in the default toolbar).
Main advantage: single click for normal export, can be changed to export all.

[octaeder]

@sunderme look here (Edit):

(animation with 4 images)

• You can click on the button showing Export by default and the dialog asking for the target path+name opens.
• Clicking on the arrow also allows to choose Export all and the dialog asking for the target directory opens.
• The toolbutton shows the last action selected.
• Moving the toolbar to the left not only gives a better look, also buttons Browse and Import are now next to each other. This seems to be reasonable since they do basically the same (import).

Maybe interchange Browse and Import?

[sunderme]

i have taken your code and implemented it with an apropriate toolbutton on dev