Fix dependencies

FIXES: https://github.com/ukf/mdrpi-match-idp-ext/issues/5
Git setup: ignores
Architecture: Rename classes to reflect specificity of the filter

MdrpiFilter* -> RegistrationAuthorityMatcher*

FIXES: https://github.com/ukf/mdrpi-match-idp-ext/issues/4
Hygene: Checkstyle fixes.
Configuration: use "regsitrars" not "issuers" to specify what to filter against

FIXES: https://github.com/ukf/mdrpi-match-idp-ext/issues/2
BUGFIX: Do not throw an exception if there is no <Extensions> in the peer's metadata

As discussed in https://github.com/ukf/mdrpi-match-idp-ext/issues/3

FIXES https://github.com/ukf/mdrpi-match-idp-ext/issues/3