This fixes an issue where specifying an audio device type before calling
initialise could cause a different device to become active, even if the
requested device type had usable devices.

With this change in place, a new device type will only be selected if
the current device type has no devices.

This commit removes the various compiler-specific JUCE_DEPRECATED macros and replaces them with C++14's deprecated attribute. It also removes the JUCE_CATCH_DEPRECATED_CODE_MISUSE flag as we can rely on the override specifier catching usage of these old virtual methods, and tidies up the DOXYGEN preprocessor checks as they were inconsistent across the codebase.

This fixes warnings that are emitted when building with the `-analyze`
flag enabled.