Make client thin

[cstamas]

Currently there is some heavy logic in client, but IMHO it is superfluous.
Instead, make client thin as possible:

• it should collect all maven config and create "seed" (ie. by hashing these things opaquely)
• based on "seed" select (or start) a daemon
• it should collect CWD and CLI params and send those those to daemon
• sit and wait, and let m39, m40, mXX decide what it likes or dislikes out of params

[gnodet]

The goal is to fully respect what the user environment as usually loaded by maven.

The compatibility is defined by two simple things:

• the JVM path (a String)
• a list of options (List<String>)
  The list of options is known as discriminating options. Those are options that actually make the daemon different and thus needs a different daemon.
  So we can definitely compute a hash of those strings, but that won't really simplify things, as the tricky part is to list and gather those options, not to compare those. See

  maven-mvnd/common/src/main/java/org/mvndaemon/mvnd/common/DaemonCompatibilitySpec.java

  Lines 33 to 34 in a14a1eb

  	private final Path javaHome;
  	private final List<String> options;

For point #3, I think that's what the client roughly does. Why would that be different ? Here's what is sent to the daemon:

maven-mvnd/common/src/main/java/org/mvndaemon/mvnd/common/Message.java

Lines 328 to 331 in 2b8076d

	final List<String> args;
	final String workingDir;
	final String projectDir;
	final Map<String, String> env;

Not sure to understand #4...