Add reduce button in popup

This PR contains 2 commits:

- the first add the reduce button, by default, to the header of the popup
- a refactoring of how the popup service displays the popup. Now the gaPopupService use the `toggle` property of its scope to show/hide the popup. That simplifies the code of the popup service. 


Test [here](http://mf-geoadmin3.dev.bgdi.ch/dev_reduce/prod/?lang=fr&topic=ech&bgLayer=ch.swisstopo.pixelkarte-farbe&X=238342.95&Y=728615.19&zoom=0&catalogNodes=457,477&layers=ch.bafu.biogeographische_regionen&layers_opacity=0.75)