Commands not used/supported, capability queries

Added no-op implementation for commands that are ignored by node-inspector,
e.g. CSS.enable.

Implemented (some of) capability queries called by front-end,
e.g. Worker.canInspectWorkers.

Implemented dummy Page.getResourceTree returning internal `node.js` as
toplevel frame. This file is marked as "main" in front-end source tree.

Removed the call to WebInspector._doLoadedDoneWithCapabilities()
from WebInspector.onWebSocketConnected, since it will be called
from Worker.canInspectWorkers response callback.

Also removed the call to WebInspector.showPanel() from
WebInspector.onWebSocketConnected, because panels are not created at that
time. (They are created by WebInspector._doLoadedDoneWithCapabilities(),
which will be called later.)
v8NameToInspectorUrl for `evaluate` scripts

Call to `evaluate` creates a new script with no URL.
This commit fixes v8NameToInspectorUrl so that it
returns empty string as URL in this case.
DebuggerAgent.getFunctionDetails()

Partial implementation of DebuggerAgent.getFunctionDetails(). There is no
easy way of obtaining scope-chain of the frame where the function was defined,
so we are returning an empty array for now.

Added unit-test verifying that v8RefToInspectorObject fills objectId
for functions.
Fixed DebuggerAgent.setPauseOnExceptions.

The previous version of setPauseOnExceptions did not work at all.

The current version always sends two `setexceptionbreak` requests,
one for `all` and another for `uncaught` exception type.
Code clean-up: removed unused code.

- Breakpoint class, breakpoint-related command handlers
- initial listing of breakpoints on front-end connect
- restoreSessionBreakpoints() (since front-end already restores all breakpoints
  on its own)