* Core 2.6.0+ fixes

* fix env -> config, run travis04 job

* don't duplicate free heap in frag data, use single stats struct

* fix dtostrf warnings, bump buffer sizes

* ...and even less words for fragmentation stat

- update every dynamicjsonbuffer with fixed size constructor argument
- change to ws callback registration to use a class builder (just cosmetic)
- test multiple ws data callbacks for each module
- remove some of the static strings in favour of ws data callback
- improve sensor ws callback data size, remove duplicated strings
- use static buffer in wsDebugSend
- postpone wsSend until loop, implement wsPost to allow other modules to queue message callbacks. remove Ticker based ws callbacks for data
- update WebUI files

* debug: heap fragmentation stat

* Rework method detection

- return check integral type as a result of detection instead of method type
- type-tagging instead of enable_if

* fix alias

* typo

* only need one bool_type instance

* Move heap debug into HeapStats header

- don't show fragmentation stats on the first call
- prettify fragmentation display
- pack function params into helper struct
- naming

* pass external flag instead

* add missing prototypes