Warnings

[tuminsky]

• Disable warnings for generated protobuf files (like -Wuseless_cast).
  warning: useless cast to type ‘const char*’ [-Wuseless-cast] reinterpret_cast<const char*>(value), size), GetArena());
• Disable warnings for boost lib (like -Wconversion, -Wsign-conversion, -Wold-style-cast and etc)
• Fix code sections with warnings.