[FaceRest] Add PUT method for servers

It's not tested yet.
[UnifiedDataStore] Add a wrapper function for DBClientConfig::getTargetServers()
[testDBClientConfig] Fix order of functions
[testDBClientConfig] Add a test for updating a server
[testDBClientConfig] Add a test for failed case of updating a server
[testDBClientConfig] Remove needless code
[testDBClientConfig] Add tests for no privilege cases of adding/updating a server
[testDBClientConfig] Fix a wrong privilege in 11e53c0
[testFaceRest] Fix inappropriate privilege for a test
[FaceRest] Add a test for PUT method of "/servers"

This commit also fix a wrong existing record check in the method.
[testFaceRest] Add a missing "static" key word to an utility function
[server] Update year
[FaceRest] Fix an inappropriate check in parseUserParameter()

Should allow an empty "flags" but shouldn't allow invalid "flags"
[FaceRest] Allow empty parameters for updating a server
[FaceRest] Use more suitable variable name

forUpdate ->
allowEmpty
[FaceRest] Fix indent
[testFaceRest] Add a test for adding a server with lacked params
[client][servers] Add "Edit" buttons for each servers
[client][servers] Fix wrong privilege names in fb7b9f2
[client][servers] Fix label of maps link

Maps ->
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