Add sharing of groups between databases

* 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

src/crypto/ssh/CMakeLists.txt

@@ -0,0 +1,14 @@
+if(WITH_XC_CRYPTO_SSH)
+    include_directories(${CMAKE_CURRENT_SOURCE_DIR} ${CMAKE_CURRENT_BINARY_DIR})
+
+    set(crypto_ssh_SOURCES
+        bcrypt_pbkdf.cpp
+        blowfish.c
+	ASN1Key.cpp
+	BinaryStream.cpp
+	OpenSSHKey.cpp
+    )
+
+    add_library(crypto_ssh STATIC ${crypto_ssh_SOURCES})
+    target_link_libraries(crypto_ssh Qt5::Core ${GCRYPT_LIBRARIES})
+endif()