Change label text in song editor for "CCLI Number"

To clarify the information requested on the "Song -> Edit -> Theme, Copyright Info & Comments" tab, the "CCLI Number" should be changed to read "CCLI Song Number".

Some people may confuse "CCLI Number" in song editing with the church-wide CCLI Number used in "Settings->General->CCLI Details-> CCLI Number"

NOTE: Songs plugin is using the same UI string label as the settings UI string - need to change so it's a separate UI string
Target: Songs plugin - openlp.plugins.songs.forms.editsongdialog.py
Target: UI Strings - openlp.core.common.uistrings.py

Target: Documentation - http://manual.openlp.org/songs.html (towards bottom ath Song Editor -> Theme, Copyright Info & Comments