is_MCT flag harmonization

There exists in the framework an indication (a flag) of whether hMCT handle is initialized or not. I noticed the following names of this flag:

• is_mct – 65 occurrences
• isMCT – 24 occurrences
• is_MCT – 12 occurrences (encoder only)
• MCT_flag – 12 occurrences (decoder only)
• hMCT_flag – 4 occurrences

I propose to get them harmonized and propose a common name MCT_flag.