…s like normally done on shells like bourne shell

Make `PluginResultsService` a unified class and service to handle sending of plugin commands to the execution service, receiving the results of plugin commands back from the execution service and sending immediate or pending results back to the plugin host.

…er`.

- Changed `ResultsService` service name to `PluginResultsService`.

- Moved `getVersionCode()` function to `PluginUtils` class.

… and `TermuxAppUtils` util classes.

…ger` util class.

- Added support to store `log_level` persistently in android `QueryPreferences` using `QueryPreferences` util class.

…ory, provided that `allow-external-apps` property is set to `true` by the user in `~/.termux/termux.properties` file.

- Added support for working directory.
- Adding support for users to set plugin `logcat` log levels to help with debugging through the configuration activity options menu.
- Added support to automatically clear `%errmsg`, `%stdout`, `%stderr` and `%result` variables when plugin action is run.
- Adding support for showing warnings in configuration activity and returning error messages via `%errmsg` to plugin host app on invalid plugin configuration or missing permissions or access failures.
- Updated `FireReceiver` to use `PluginResultsService` for sending commands to execution service and to send error messages to plugin host app if required.
- Updated default action timeout value to `10s` regardless of `inTerminal` value.
- Removed requirement for `TASKER_DIR` to exist for plugin configuration since absolute paths are allowed.
- Fixed `isBundleValid()` function.

- Changed `case` statements to `if` since resource IDs are non-final from gradle plugin version `5`.

- Updated library versions and switched to `AndroidX`.