Correct the plural forms for Manx (Gaelg)

Correct the plural forms for Manx (Gaelg)

Backported the plural rules from CLDR 24 as an override to CLDR 23 rules
exising in MediaWiki. The syntax for plural rules changed in CLDR 24, so
modified the syntax to fit the CLDR 23 syntax

Once we are ready with the updated parsers for CLDR 24(See bug 56931),
we should remove the override.

Since we remove the custom plural forms in MW in favor of CLDR,
the following changes comes into effect:

1. 'few' form used as 'zero' form in MW. Practially that make 'one' form used
as 'two' form and 'two' used as 'few' form.
This breaks existing gv {{PURAL}} usage as dicussed in the bug report

2. CLDR defines 'few' form as n % 100 = 0,20,40,60 but MW adds 80 also to that
list, ie  n % 100 = 0,20,40,60, 80. So with this patch, 80 is no longer considered
as 'few' plural form.

Bug: 47099
Change-Id: I46ab3dadc7fe08c1e60bbd81a1ee841e166e9608