Removed unnecessary implementation of deleting a temp file since there was already support for this.

Refactored unit tests to not use temp dir (does not work reliably).

Fixed bug in class DelegateReadWriteRConnection: Did not properly return the output stream for compatibility.
Ignored a test using JUnit's Ignore annotation.

Added method 'ByteBuffer getChannel()' to interface RConnection and therefore exposing the unterlying channel for FastR internal use.
Removed fall-through cases in FileConnections.

Replaced "RError.error(this..." by "RError.error(RError.SHOW_CALLER...".
Implemented handling of flag 'raw' when opening files.
Added a test for this.
Fixed warning in class ConnectionFunctions.

Refactored base classes RConnection, BaseRConnection, and DelegateRConnection to strictly seperate the concerns.
BaseRConnection now stores "session data" whereas a delegate connection performs the I/O operation.
RConnection is now just an interface defining common operations.

Merged tests for raw connections into TestConnections.

Fixed checkstyle errors.

Implemented non-blocking/text-mode behavior of function "readLines" (silently pushes back incomplete final lines).
Refactored all delegate connection implementations to be based on a channel (again).

Added micro tests for several combinations of readLines' flags.

Splitted delegate connection classes into blocking and non-blocking implementations (at least prepared for non-blocking).
This was necessary because we cannot simply wrap channels into input streams on non-blocking sockets.

Implemented proper dispatching if an URL is used in function "file".

This seems not to be easily possible from Java.
Added more tests and implemented some small missing functionality.
Refactored file and compressed file connection implementation.
Added encoding support for files.
Made some cleanup.

- Moved DelegateRConnection and subclasses into separate files (for better overview).
- Increased code sharing of readLines, readChar, readBin (same for write) by providing standard implementation in the delegate classes. Hence, implementation of, for example, named pipes (FIFOs) is almost trivial.
- Fixed some bug in SeekableMemoryByteChannel and changed behavior if a byte array is provided in the constructor.
- Implemented push back reset when seeking.

Added initial test class for FIFOs and added tests to file and text connections.
Implemented function "fifo" for working with named pipes.

[GR-2982] Remove temporary directory on context exit; share parent tempdir for SHARED_PARENT_RW contexts.