[kernel] Make capabilities/handles global

Instead of handles / capabilities having numeric ids that are only valid
for the owning process, they are now global in a system capabilities
table. This will allow for specifying capabilities in IPC that doesn't
need to be kernel-controlled.

Processes will still need to be granted access to given capabilities,
but that can become a simpler system call than the current method of
sending them through mailbox messages (and worse, having to translate
every one into a new capability like was the case before). In order to
track which handles a process has access to, a new node_set based on
node_map allows for an efficient storage and lookup of handles.

src/kernel/kernel.module

@@ -11,6 +11,7 @@ kernel = module("kernel",
         "apic.cpp",
         "assert.cpp",
         "boot.s",
+        "capabilities.cpp",
         "clock.cpp",
         "cpprt.cpp",
         "cpu.cpp",