Various improvements for ILogcatViewerService

[dgburr]

• Allow building with more recent SDKs
• Export services so that they are accessible by external applications
• Add optional callback mechanism so external applications can receive notifications via IPC
• Add support for optional filter specifications/message filters
• Allow the logcat process to be terminated without waiting for it to produce additional output (which might not happen for a long time/if at all if any filters have been specified)