Make 0.4.x the master branch

[laserval]

Internally at Findwise the 0.4.x branch is still the major version used, and we have had a hard time moving to 0.5.0.

The suggestion for now is to move 0.4.x to master and make the current master a 0.5.x branch instead. This is unfortunate for continued development of Hydra, but it reflects the current state of the project better.

[ebbesson]

We should do this!

[Nycander]

This issue is starting to become rather urgent!

[leonardsaers]

+1