.gitignore: Add Kdevelop4 project files

I'm not sure what is the costume with such IDE project files.
Most might be dot-files. It is kind of annoying for the Kdevelop4 user.

So please consider adding *.kdev4 files to be ignored?
Signed-off-by: NBoaz Harrosh <boaz@plexistor.com>
[mmarek: Moved at the and and added a comment]
Signed-off-by: NMichal Marek <mmarek@suse.cz>

.gitignore

@@ -96,3 +96,6 @@ x509.genkey
 
 # Kconfig presets
 all.config
+
+# Kdevelop4
+*.kdev4