[IndexedDB] WebIDL-related spec nits

(Note, I did not include the various things relating to keyPath that I
mentioned last week, because I do not consider those to be trivial changes).

Globally, the spec is inconsistent about whether the prose is in the same
order as the IDL, or whether the prose is in alphabetical order.  I would
prefer the former, but consistency of some sort is desirable.

3.1.9

The return type of the static functions on IDBKeyRange is not 'static
IDBKeyRange', it is just 'IDBKeyRange'.

3.2.1

The correct type name is "object", not "Object" (note the capitalization).

IDBRequest.readyState should be an enum type, not a DOMString.

3.2.2

IDBVersionChangeEvent should probably reference whatever spec defines how
constructors work for DOM events.

3.2.4

IDBDatabase.transaction's mode argument should be an enum type, with a
default value specified in IDL instead of in prose.

3.2.5

Is it intentional that IDBObjectStore.indexNames does not return the same
DOMStringList every time, unlike IDBDatabase.objectStoreNames (yes, I
realize that the circumstances under which the former can change are much
broader).

IDBObjectStore.openCursor's direction argument should be an enum type, with
a default value specified in IDL (right now it is unspecified).

3.2.6

IDBIndex.openCursor and IDBIndex.openKeyCursor's direction argument should
be an enum type, with a default value specified in IDL.

3.2.7

"Object" should be "object".

3.2.8

IDBTransaction's mode attribute should be an enum type.

Also, it would be nice if we could tighten up keys from 'any' to a union.

- Kyle