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 change adds the examples from `examples/Plugins` to the
AudioPluginHost, surfacing them as 'internal' plugins in the popup menu.

We also build this into the AudioPluginHost, as a convenient way to
check the midi outputs of plugins and devices.