Introduce modification-based change tracking in BulkFileWatcher to
reduce emitted signals caused by file changes within the same directory.
Resolves#2895.
BulkFileWatcher emitted multiple file change signals (like
QFileSystemWatcher) for the watched files. Introduced a delay by waiting
until the end of the event loop to aggregate signals emitted by
QFileSystemWatcher before emitting custom signals.
* Add source folder keeshare for sharing with corresponding define WITH_XC_KEESHARE
* Move common crypto parts to src/crypto/ssh
* Extended OpenSSHKey
* Move filewatching to own file (currently in two related classes DelayedFileWatcher and BulkFileWatcher)
* Small improvements for style and code in several classes
* Sharing is secured using RSA-Keys which are generated on demand
* Publisher signs the container using their private key
* Client can verify the signed container and choose to decline an import,
import only once or trust the publisher and automatically import all
data of this source henceforth
* Integration of settings into Group-Settings, Database-Settings and Application-Settings
* Introduced dependency QuaZip as dependency to allow combined export of
key container and the (custom format) certificate
