Allow operations between CHEBTECH and FOURTECH.
1. Creation of two classes PERIODICTECH and NONPERIODICTECH between SMOOTHFUN and FOURTECH/CHEBTECH. PERIODICTECH is an abstract class with parent SMOOTHFUN and child FOURTECH. NONPERIODICTECH is an abstract class with parent SMOOTHFUN and child CHEBTECH. These two classes have a method ISPERIODIC that returns always 1 for PERIODICTECH and 0 for NONPERIODICTECH.
2. Modifications of +,-,*,/ in CHEBFUN.
1. Adjust the domains.
2. Add tests.
1. Rename isperiodic -> isPeriodicTech.
2. Add a isPeriodicTech for SINGFUNs.
3. Modify tolerances in the tests.
Implement isPeriodicTech at the fun level.
Forgot to delete a few commented lines.
some minor changes to help text and comments.
Merge pull request #1170 from chebfun/feature-fourtech-chebtech

Allow operations between FOURTECH and CHEBTECH.