Alter constants to use common style

[joeljfischer]

Bug Report

Currently our constants appear to be defined in a variety of styles.

// SDLRPCPayload
const NSUInteger RPC_HEADER_SIZE = 12;

// SDLIAPSession
NSString *const IOStreamThreadName = @"com.smartdevicelink.iostream";
NSTimeInterval const streamThreadWaitSecs = 1.0;

// SDLIAPTransport
NSString *const LegacyProtocolString = @"com.ford.sync.prot0";
NSString *const ControlProtocolString = @"com.smartdevicelink.prot0";
NSString *const IndexedProtocolStringPrefix = @"com.smartdevicelink.prot";
NSString *const MultiSessionProtocolString = @"com.smartdevicelink.multisession";
NSString *const BackgroundTaskName = @"com.sdl.transport.iap.backgroundTask";

Expected Behavior

The SDLIAPTransport style.

Observed Behavior

A variety of styles