list: added decrement size when removing node

Forgot to decrement the size of the list when a node is removed.

Signed-off-by: Joel Nider <joel@nider.org>
ui: added DestroyUI and DeleteButton functions

Two missing functions - one was in the header and not implemented, the
other not implemented and not in the header.

Signed-off-by: Joel Nider <joel@nider.org>
list: missed a return statement in ListCreate()

Don't know why the compiler didn't warn me about this one. The list was
being created correctly, but I wasn't returning the node to the caller.
Better check my compiler flags as well.

Signed-off-by: Joel Nider <joel@nider.org>
Added 'id' to ifel and each Create() function

The ID field uses the same name as a previous field which has been
renamed to 'type'. the new ID field is a user-defined indentifier
for the UI object. It is used in callbacks & events so the user can
differentiate between various UI objects.

Signed-off-by: Joel Nider <joel@nider.org>
ui: added null pointer check

Check for a null pointer when deleting a button

Signed-off-by: Joel Nider <joel@nider.org>
consolidated UI id's

all UI objects now have a application-wide unique ID. Makes things
a bit easier to determine which object is in focus and what received
the event.

Signed-off-by: Joel Nider <joel@nider.org>