- Some refinement for file data source
- Add resource name checking in FlowRuleManager to avoid NPE

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

- Add method to check if the resource is modified in `AutoRefreshDataSource`
- Implement FileWritableDataSource

- Add `close` method in WritableDataSource (to extend AutoCloseable in JDK 1.7 later)
- Separate the writable file data source from original class
- Add a sample to show how to register data sources via Sentinel init mechanism
- Separate a writable data source registry from original handler to make it clear

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

- Spilt DataSource into two types: ReadableDataSource and WritableDataSource
- The AbstractDataSource now is read-only
- Refactor the file data source for writable implementation
- Rename: ConfigParser -> Converter (represents both encoder `T -> S` and decoder `S -> T`)
- Some other refinement

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

* Use named thread factory with all thread pools for identification

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

Signed-off-by: Eric Zhao <sczyh16@gmail.com>