Perform elementary conversion of log4j constructs with slf4j. It also replaces the usage of `fatal` with `error` methods and calls `toString` on objects passed by parameter to logger methods.

This commit doesn't touch classes into:

- Applications
- Archives
- Tests

It also leaves frameworks not built by Maven intact.

AjaxRemoteLogging component doesn't support the log level `fatal` anymore. In contrast, `trace` was added as a log level option.

I'm not happy with this change. Anyway, I removed this option because it's impossible to change the log level using slf4j in runtime without knowing the underlying log library being used.

The log level was set as `Level.WARN` in the `WOHelperFunctionDeclarationParser`, `WOHelperFunctionHTMLParser` and `WOHelperFunctionTagRegistry` classes. This configuration was removed because it's impossible to set the log level in runtime using slf4j.

The `ERD2WPage` component uses `log4j` Nested Diagnostic Context (NDC) statements, which `slf4j` doesn't support. For this reason, we're migrating to Mapped Diagnostic Context (MDC) statements.

The `com.webobjects.appserver._private.WOCGIFormValues.Encoder` class of the `JavaWebObjects` framework creates a `org.apache.log4j.Logger`. Since we can't modify this class, I had to copy it into the `ERExtensions` framework—to supersede the original class—and reference the `org.slf4j.Logger` interface.

…rt multiple logging libraries

The `ERXLogger` class now implements the `org.slf4j.Logger` interface instead of extending the `org.apache.log4j.Logger` class. It's not connected to `log4j` in any sense anymore.

Add a new `ERXNSLogSlf4jBridge` class to make the bridge between `NSLog` and `slf4j`.

Move the re-initialization of `log4j` console appenders to the new class `ERXLoggingUtilities` and execute this code only if `log4j` is the chosen `sfl4j` binding.

Support setting the log level using distinct log libraries via the `ERXLoggingUtilities` class.

Side-effects:

- Remove the ability to configure a custom subclass of `ERXLogger` using the `er.extensions.erxloggerclass` property.
- Remove the `er.extensions.logging.ERXLogger.Factory` class since it implements `org.apache.log4j.spi.LoggerFactory`. Thus, it's not possible to define a custom `ERXLogger` factory anymore.

Replace `org.apache.log4j.lf5.util.StreamUtils` with `org.apache.commons.io.IOUtils.copy` on `ImageMagickCommandlineMetadataParser`.

…mode

Now, Wonder can change the log level of a few logging libraries: log4j 1, reload4j, log4j 2, and logback.

The wonder-bom groups all WebObjects and Wonder dependencies into one pom. It also excludes `JavaXML` as a transitive dependency of the `JavaWebObjects` dependency. `JavaXML` has also been removed as a direct dependency of all frameworks.

The removal of the JavaXML transitive dependency from both applications caused NoClassDefError exceptions. This commit adds the Apache Xerces as an explicit dependency to both projects.