implement the "testable mode" in which the application can be paused and resumed by the test routine

Added a TestDecoratorRegisterAccessor which is optionally put around accessors to facilitate test of applications. This TestDecoratorRegisterAccessor does not yet do anything, functionality will be added in the next commits.

fixed replacing Array and ScalarAccessors, which was broken after moving to the NDRegisterAccessorBridge-based accessors

fixed poll-type inputs using no longer non-blocking read after the switch to the NDRegisterAccessorBridge-based accessors

Rebased the ScalarAccessor and ArrayAccessor classes onto the mtca4u::NDRegisterAccessorBridge class.
Known problems present: code compiles but tests do not run

Changed the FeedingFanOut so that it does not extract the meta-data (name, shape etc.) from the first slave but expects it in the constructor. This is necessary since the meta-data is already given by the application.

fixed variable networks with external trigger not being put into the same TriggerFanOut (which is required since they should be in the same TransferGroup)

- add all networks triggered from the same node to the same TriggerFanOut
- put all feeding nodes in a TriggerFanOut into the same TransferGroup

- added some class documentation

- some more code cleaning

fixed blocking read transfer for the constant accessor: should only return on first read and then block forever

Forward declaration is taken from DeviceAccess header file, which solves problems if classes are moved to another namespace.

Use mtca4u::setDMapFilePath() instead of the BackendFactory's member function. Since all applications will need it, the corresponding header file is now included in ApplicationCore.h

Removed the macros for defining accessors and introduced convenience classes instead. This adds slightly more syntactic sugar, but also allows more flexibility and seems to be a more coherent interface.

This commit incompatibly breaks the interface with the previous versions. Since ApplicationCore is not yet used in any productive environment, no compatibility is provided.

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67054

- Default constructor for Accessor exists now
- A function Accessor::replace() allows to assign a new accessor
- For clarity/safety: copying accessors using the assignment operator is now forbidden
- The destructor of the accessor unregisters it from the module (to allow temporary accessors)

changed the internal thread implementation to boost::thread and make use of the interruption points to properly terminate the application

use NDRegisterAccessor class instead of ProcessArray, so that e.g. the ConstantAccessor works as well

Fixed a bug that a pointer to a temporary VariableNetworkNode object was sometimes stored (as a trigger receiver or source). Instead now an object with the same data pointer inside is stored.