CA_ROOT_CERTIFICATE defined as a global variable

[csgregg]

CA_ROOT_CERTIFICATE is defined as a global in ThingerClient.h, so makes the library difficult to use when needing to add to multiple files in the same build. Possible solutions - 1) change CA_ROOT_CERTIFICATE to a #define instead of a global variable. 2) pass the cert in the constructor and let the user define the correct cert...