Remove superfluous TODO

The below is obviously already implemented :)
Fix FSStoragePlugin_test::testGetObjectPropertyValueFromStorage()

Keys in m_pathNamesMap that are directories don't have the '/' suffix;
m_pathNamesMap["/tmp/mtptests/"] was giving correct result by pure
chance because storage root has a handle 0, which is accidentally the
same as the default value QMap returns here.
Fix testInotifyModify() to actually test file modification

How the test was written, the file could have been just created for it
to pass. New implementation first tests the file exists and then checks
that its size before and after modification changes.
Fix clean build

fsstorageplugin.so now depends on libmeegomtp.so, so adding
CONFIG += ordered to ensure mtpserver target is built before
mts_fsstorage_plugin.
Add inotify watch to all directories

By mistake, addWatchDescriptor() was called only when the directory was
being created in FSStoragePlugin::addToStorage().

Reworked FSStoragePlugin_test::testInotifyCreate() to cover this bug.