Remove centering for floats (#364)

This was a bad idea...:
https://tex.stackexchange.com/questions/2651/should-i-use-center-or-centering-for-figures-and-tables

floatrows not sure how it should work with flowcharts... so we use
centring

I don't want to redefine all floats either as we use them for chapters
title page.

book/history/sourdough-history.tex

@@ -26,7 +26,7 @@ waters, another single-celled life form, \emph{archaea}, also thrived. These
 organisms inhabit extreme environments, from boiling vents to icy waters.
 
 \begin{figure}[!htb]
-\begin{center}
+\centering
   \input{figures/fig-life-planet-sourdough-timeline.tex}
   \caption[Sourdough microbiology timeline]{Timeline of significant events
     starting from the first day of Earth's existence,
@@ -34,7 +34,6 @@ organisms inhabit extreme environments, from boiling vents to icy waters.
     marked at midnight. This visualization shows the pivotal steps
     of life and sourdough on earth.}%
   \label{fig:planet-timeline}
-\end{center}
 \end{figure}
 
 Whoever comes first, bacteria or archaea, remains debated. For three
@@ -70,12 +69,11 @@ Ancient Jordan~\cite{jordan+bread}. Looking at the earth's timeline sourdough
 bread can be considered a very recent invention.
 
 \begin{figure}[!htb]
-\begin{center}
+\centering
   \input{figures/fig-sourdough-history-timeline.tex}
   \caption[Sourdough history timeline]{Timeline of significant discoveries and
   events leading to modern sourdough bread.}%
   \label{fig:sourdough-timeline}
-\end{center}
 \end{figure}
 
 The exact origins of fermented