Add OstreeAsyncProgress, use it for ostree_repo_pull

Several APIs in libostree were moved there from the commandline code,
and have hardcoded g_print() for progress and notifications.  This
isn't useful for people who want to write PackageKit backends, custom
GUIs and the like.

From what I can tell, there isn't really a winning precedent in GLib
for progress notifications.

PackageKit has the model where the source has GObject properties that
change as async ops execute, which isn't bad...but I'd like something
a bit more general where say you can have multiple outstanding async
ops and sensibly track their state.

So, OstreeAsyncProgress is basically a threadsafe property bag with a
change notification signal.

Use this new API to move the GSConsole usage (i.e. g_print()) out from
libostree/ and into ostree/.

tests/test-sysroot.js

@@ -68,7 +68,7 @@ sysrootRepoConfig.set_string(testosRefSection, 'url', 'file://' + upstreamRepo.g
 sysrootRepoConfig.set_boolean(testosRefSection, 'gpg-verify', false);
 sysrootRepoConfig.set_string_list(testosRefSection, 'branches', [runtimeRef]);
 
-sysrootRepo.pull('testos', null, 0, null);
+sysrootRepo.pull('testos', null, 0, null, null);
 
 //// TEST: We can deploy one tree
 
@@ -111,7 +111,7 @@ sysroot.write_deployments(newDeployments, null);
 
 libtestExec('os_repository_new_commit');
 
-sysrootRepo.pull('testos', null, 0, null);
+sysrootRepo.pull('testos', null, 0, null, null);
 
 let [,newRev] = upstreamRepo.resolve_rev(runtimeRef, false);
 
@@ -137,7 +137,7 @@ print("OK two deployments");
 
 libtestExec('os_repository_new_commit 0 1');
 
-sysrootRepo.pull('testos', null, 0, null);
+sysrootRepo.pull('testos', null, 0, null, null);
 
 let [,thirdRev] = sysrootRepo.resolve_rev(runtimeRef, false);
 assertNotEquals(newRev, thirdRev);