Some more simplifications.
Merge branch 'fix-chebgui-IVPs-3' of github.com:chebfun/chebfun into fix-chebgui-IVPs-3
Changing default export names to chebbvp, chebeig, chebivp and chebpde.

Closes #1257.
Lot of fontsize changes related to PDEs in the GUI.