Introduce "Folder" data source

[Kittyfisto]

The problem:
The user wants to sift through dozens of log files which are written to a directory subtree. The list of log files can be subject to change (rolling file appenders, app might auto delete old log files).

With the current setup, a user has to manually drag and drop N files into Tailviewer, organize them into a group. When new files are created, the user has to add them all manually. This is freaking tedious when the amount of log files approaches hundreds.

The solution:
A user shall be able to add a folder source to Tailviewer. The following behaviour applies:

• Files which have been added to the folder (or a sub-folder) are automatically added as child data sources to the folder in the data source tree within .5 seconds
• Files which have been deleted are removed within .5 seconds
• The settings of a child data source are NOT forgotten when its file is removed from disk. Instead all settings shall be persisted forever (until the folder source is removed)
• When a previously deleted file appears again, then ALL previous settings are immediately applied again (activated filters, search, log level filters, follow tail, the simply everything)
• A folder data source presents a merged view onto all of its children (again, recursively)
• Only the top level folder data source can be removed. Doing so removes itself and all of its children immediately
• Child data sources of a folder data source cannot be removed from the tree like normal file data sources (the user has to delete the file on disk)
• Dragging a folder into Tailviewer automatically creates a new folder data source or selects the data source if that folder has already been added before

Possible future extensions:

• Add folder configuration
  • Recursive: yes/no
  • Regular expression to define which files shall be included (does this suffice?)

UI Mockup:

Technical details

• This feature only makes sense when merging many files becomes way faster: The current implementation takes ages to merge 20+ files - this must be due to
  • One o more bugs in the MergedLogFile merge implementation
  • A suboptimal algorithm to merge log file deltas
• Re-use folder watches and other I/O related stuff from https://github.com/Kittyfisto/System.Extensions

[Kittyfisto]

TODO:

• Align all input fields along one line (export folder, scroll speed, font size, folder data source pattern)
• Settings make descriptive text slightly more grey
• Move descriptive text to be completely under the text box
• Folder data source should mention total number of files and number of files which match filter (e.g. 10 of 30 files)
• If limit of 256 files is reached, a folder data source should print a warning
• Child data source should print only print path relative to its folder data source
• Improve error message when a folder data source doesn't contain any files
• Improve error message when the pattern of a folder data source causes no files to be matched
• Add folder data source specific configuration
• Configure path, recursive and pattern of folder data source
• Allow drag 'n drop of folders from explorer
• If a change in configuration does not result in a different set of data sources, then the merged data source should NOT be re-created (requires change in IFilesystem library)
• Data sources cannot be dragged onto merged folder sources
• Data sources cannot be dragged out of merged folder sources
• Ensure bookmarks can be set on a folder data source