Typo fixes

+ User facing typos
+ trivial source comment typos
+ superflous double whitespace issues
+ found redundant comment typo
Found using `codespell -q 3 --skip="./build/wix/Localization,./res/translations,./lib" -I ../mixxx-whitelist.txt` where the contents of the whitelist were:
```
iff
freee
substract
```

1 files changed, 1 insertions, 1 deletions

diff --git a/src/library/library.cpp b/src/library/library.cpp
index 5a22fe9f84..7d94a9c9d4 100644
--- a/src/library/library.cpp
+++ b/src/library/library.cpp
@@ -52,7 +52,7 @@ const QString Library::kConfigGroup("[Library]");
 //static
 const ConfigKey Library::kConfigKeyRepairDatabaseOnNextRestart(kConfigGroup, "RepairDatabaseOnNextRestart");
 
-// This is is the name which we use to register the WTrackTableView with the
+// This is the name which we use to register the WTrackTableView with the
 // WLibrary
 const QString Library::m_sTrackViewName = QString("WTrackTableView");