Replace Poco::RegularExpression with boost::regex

Refs #10603
Use boost::regex_search and not boost::regex_match

The latter requires everything to match, but we just want to search within
a string. This is more like what Poco did.
Refs #10603
Merge pull request #74 from mantidproject/bugfix/10603_eqsansload_regex

Switch to boost::regex in EQSANSLoad