This fixes an issue with boost == 1.60.0

- use suitable DefaultEpsilon for each style
- use macro DXTC_EXPECT_FLOAT_* where possible

Drop unused guards and includes, simplify implementation of is_complex,
add missing include.

Conflicts:
	dune/xt/common/test/float_cmp.cc

You now have to write
```
DXTC_has_typedef_initialize_once(Bar);
```
instead of
```
DXTC_has_typedef_initialize_once(Bar)
```
which makes it easier for some tools to digest this piece of code.