Added algorithm helper class. Refs #8322.

- This class reduces the code across algorithms.
Refactored `CatalogSearch`. Refs #8322.

- Removed unused attributes from `CatalogSearchParam`.
- Updated `ICat3Helper.cpp` to work correctly with new interface (e.g. when "my data" is checked).
- Updated documentation for algorithm.
Tidied `CatalogSearchParam` class. Refs #8322.

- Removed unnecessary comments in header. Made them more concise and consistent with other header files in Mantid.
- Removed RB number search as it is no longer used in the interface.
- Added investigator surname search back to `CatalogSearch`.
Tidied up `CatalogMyDataSearch`. Refs #8322.

- Removed unused headers and added call to helper class.
Refactored catalog logout algorithm. Refs #8322.

- Removed unimplemented method `doLogout()`.
Tidied Catalog login algorithm. Refs #8322.

- Removed unnecessary catalog error method.
Updated CatalogListInstruments. Refs #8322.
Made use of algorithm helper class. Refs #8322.

- Removed unused methods (`filterLogFiles` & `isDataFile`) and related properties.
Use algorithm helper class. Refs #8322.

- Updated documentation for each algorithm and tidied header files.
Updated `CatalogDownloadDataFiles`. Refs #8322.

- Added call to helper class and removed un-used headers.
- Removed `using` Poco namespaces as each are only called once or twice in the download method.
Added datafileName & removed investigation abstract. Refs #8322.

- Previously, the functionality existed to search by datafile name, but was not implemented on the interface. I have re-added this functionality (removed it in a previous commit), and replaced the investigation abstract on the GUI with datafile name.
- I removed all references to investigation abstract search.
Merge remote-tracking branch 'origin/master' into feature/8322_icat_refactor_algorithms
Merge remote-tracking branch 'origin/master' into feature/8322_icat_refactor_algorithms. Refs #8322.

Conflicts:
	Code/Mantid/Framework/ICat/inc/MantidICat/CatalogSearchParam.h
	Code/Mantid/Framework/ICat/src/CatalogSearchParam.cpp
Merge remote branch 'origin/feature/8322_icat_refactor_algorithms'