Add Multi key sequence definitions for double grave and inverted breve

Without specifically having bound the dead keysyms for these diacritics, these characters would normally be untypable. The nomenclature here is based on existing sequences for cyrillic letters with double grave as well as ones like "a(" etc. for certain letters with regular breve

Signed-off-by: jmcwilliams403 jmcwilliams403@gmail.com