Add Multi_key counterparts to BÉPO dead kkeys

Originally, dead_greek and dead_currency were additions meant for the BÉPO layout, with other layouts since implementing one or both of these keysyms later on (for example, EurKEY). However, users of other common national or international layouts have not been able to enjoy these sequences, but may posses the non-dead character which these dead keysyms represent (I.E. currency and mu). This commit allows users of non-BÉPO layouts to type these sequences given they possess the specific Latin-1 characters which represent them.