Fix regex for ActorPath so it can handle escaped characters correctly

Escaped characters, i.e. % hex hex, for example "%2a" should be matched by the regex, but the regex used the named Unicode character class N. Like this
    %\p{N}{2}
i.e. percent followed by exactly two characters from the named Unicode character class N, All Numbers.

The problem with that character class is that it also contains other number characters, such as Ⅷ⅓, so "%Ⅷ⅓" was matched by the regex.
However the character class do not contain the hexadecimal letters a-f so "%2a" was not allowed.

Changed
    %\p{N}{2}
to:
    %[0-9a-fA-F]{2}

Allow usage of parenthesis ().
Note that AKKA JVM does not allow parenthesis ( ) but, according to RFC 2396, those are allowed and since we use URL Encode (see Akka.Remoting.AddressUrlEncoder) to create valid actor names, we must allow them too.
Merge pull request #519 from HCanber/fix-remotewatcherspec

Fix regex for ActorPath so it can handle escaped characters correctly