[System.Core/Android] Update TimeZone database self test.

Add Makefile rules to automagically download the TimeZone database
from the Android target $(ADB_TARGET), and build the tzi.exe app.

	$ make android-dump-tzdata ADB_TARGET=-d
	# downloads timezone data into ./android/tzdb.
	# dumps timezone data into ./android/tzdata
	# builds ./tzi.exe

	# Show adjustment rules for a given timezone dump
	$ mono tzi.exe -i=tzdata/Asia/Amman

Add `tzi.exe -R` option to show the TimeZoneInfo.GetAdjustmentRules()
output for all encountered timezones.

Add `tzi.exe -o=PATH` option to dump the TimeZone data to disk for
interrogation.

Add `tzi.exe -i=PATH` option to read in the specified TimeZone data
file and dump the rules contained therein.

Update usage comments.