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/widget/wpushbutton.cpp b/src/widget/wpushbutton.cpp
index 9468b5bb21..a7a4b1726d 100644
--- a/src/widget/wpushbutton.cpp
+++ b/src/widget/wpushbutton.cpp
@@ -379,7 +379,7 @@ void WPushButton::mousePressEvent(QMouseEvent * e) {
             // or this is a push button.
             emitValue = 1.0;
         } else {
-            // Toggle thru the states
+            // Toggle through the states
             emitValue = getControlParameterLeft();
             if (!isnan(emitValue) && m_iNoStates > 0) {
                 emitValue = static_cast<int>(emitValue + 1.0) % m_iNoStates;