i2c: Various fixes to make the PD suitable for GUIs.

i2c: Various fixes to make the PD suitable for GUIs.

The output format of the slave address is now a PD option. It can be
"shifted" or "unshifted", i.e. bit 0 (which contains a read/write
marker) is either shifted out or not, i.e., the slave address is
displayed as 8bit or 7bit number (or 11bit/10bit number for 10bit slave
addresses).

Data bytes (not address bytes) are always shown as 8bit values, of course.

Add annotation types for the individual I2C components such as
start conditions, stop conditions, ACK/NACK, address read/writes,
data read/writes and so on.

This fixes bug #151.