Rename skydb to mojodb

The skydb tool is actually used to run many mojo apps that aren't related to
Sky.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1164023004

HACKING.md

@@ -9,18 +9,18 @@ Building
 Running applications
 --------------------
 
-* ``./sky/tools/skydb start out/Debug [url]``
+* ``./sky/tools/mojodb start out/Debug [url]``
 
-    `skydb` has numerous commands, visible via `skydb help`.  Common ones include:
-    * `skybd start` BUILD_DIR [url]
-    * `skydb load` [url]
-    * `skydb stop`
-    * `skydb start_tracing` # Starts recoding a performance trace (use stop_tracing to stop)
-    * `skydb print_crash` # Symbolicate the most recent crash from android.
+    `mojodb` has numerous commands, visible via `mojodb help`.  Common ones include:
+    * `mojodb start` BUILD_DIR [url]
+    * `mojodb load` [url]
+    * `mojodb stop`
+    * `mojodb start_tracing` # Starts recoding a performance trace (use stop_tracing to stop)
+    * `mojodb print_crash` # Symbolicate the most recent crash from android.
 
-Once `skydb start` is issued, all subsequent commands will be sent to
+Once `mojodb start` is issued, all subsequent commands will be sent to
 the running mojo_shell instance (even on an attached android device).
-`skydb start` reads gn args from the passed build directory to
+`mojodb start` reads gn args from the passed build directory to
 determine whether its using android, for example.
 
 * ``./sky/tools/test_sky --debug``