Move logic from GitWebType to GitWebConfig

GitWebType is a dumb POJO. Initialization of this type was split
across GitWebType and GitWebConfig for no strong reason, possibly
related to the fact that GitWebType is in the gerrit-common package
and so can't depend on the JGit Config object.

The setters of GitWebType weren't behaving like normal POJO setters,
as they were ignoring null or empty values. Get rid of this
special-casing behavior, which made the behavior of GitWebConfig
difficult to understand.

Instead, move all the construction of a GitWebType to GitWebConfig,
which is a server-side class and can handle the Config parsing as well
as the named default configurations.

Change-Id: I119778c3ab3b791fbf363e2d87818e40dc9687b6

gerrit-common/src/test/java/com/google/gerrit/common/data/EncodePathSeparatorTest.java

@@ -19,21 +19,15 @@ import static org.junit.Assert.assertEquals;
 import org.junit.Test;
 
 public class EncodePathSeparatorTest {
-
   @Test
   public void testDefaultBehaviour() {
-
-    GitWebType gitWebType = GitWebType.fromName(null);
-
-    assertEquals("a/b", gitWebType.replacePathSeparator("a/b"));
+    assertEquals("a/b", new GitWebType().replacePathSeparator("a/b"));
   }
 
   @Test
   public void testExclamationMark() {
-
-    GitWebType gitWebType = GitWebType.fromName(null);
+    GitWebType gitWebType = new GitWebType();
     gitWebType.setPathSeparator('!');
-
     assertEquals("a!b", gitWebType.replacePathSeparator("a/b"));
   }