Add the span of western years for each 60-year cycle

[christiansteinert]

It would be good to extend the labels for the dropdown of 60-year cycles ("Rabjung") so that for each cycle it is immediately visible which time period is included in this cycle.

So the dropdown for the Rabjung selection should contain values like:
1 (1076-1077)
2 (1136-1137)
etc.

The time spans for the supported rabjungs are as follows:
1076-1077 (1st Rabjung)
1136-1137 (2nd Rabjung)
1196-1197 (3rd Rabjung)
1256-1257 (4th Rabjung)
1316-1317 (5th Rabjung)
1376-1377 (6th Rabjung)
1436-1437 (7th Rabjung)
1496-1497 (8th Rabjung)
1556-1557 (9th Rabjung)
1616-1617 (10th Rabjung)
1676-1677 (11th Rabjung)
1736-1737 (12th Rabjung)
1796-1797 (13th Rabjung)
1856-1857 (14th Rabjung)
1916-1917 (15th Rabjung)
1976-1977 (16th Rabjung)
2036-2037 (17th Rabjung)
2047-2107 (18th Rabjung)
2107-2167 (19th Rabjung)
2167-2227 (20th Rabjung)