title: How to let user select a CRS in QGIS Python plugin?
body: <p>I am currently developing a QGIS Plugin in python. In it, the user should be able to select a Coordinate Reference System (CRS). In QGIS built-in dialogs, there often is this window called &quot;Coordinate Reference System Selector&quot; which allows selection of recently used CRS, as well as other Systems and also a Information box and visualisation of the Bbox of the CRS.</p>
  <p><a href="https://i.stack.imgur.com/2D4M7.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2D4M7.png" alt="CRS Selector" /></a></p>
  <p>Is there a way to replicate this? It would be very tideous to recreate all this informations and functionality. I would have excpected at least something CRS related in &quot;QGIS custom widgets&quot; in QT Designer, but I couldn't find anything.</p>
  <p>Or if this isn't possible, is there at least a way to get all CRS's to display them in a Combobox?</p>