Bugfixes, improvements and new symbols/nosymbols option for all styles (#34)

* fix Researcher ID (still) doesn't display Issue #29.
* make options 'symbols' and 'nosymbols' available to all styles to toggle whether symbols should be used or not. Include symbols in oldstyle by default.
* migrate older newcommand syntax in moderncvcollection.sty to the xparse syntax.
* Fix resumé typo in template. Is now résumé.
* remove loading lmodern fonts in all styles as they can produce issues with german characters, see https://tex.stackexchange.com/questions/496630/lualatex-problems-with-german-characters.
* remove loading inputenc package by default. Only load the package when pdflatex is used.

moderncvstylecasual.sty

@@ -17,8 +17,13 @@
 \DeclareOption{left} {\edef\moderncvstyleheadoptions{\moderncvstyleheadoptions,left}}
 \DeclareOption{right}{\edef\moderncvstyleheadoptions{\moderncvstyleheadoptions,right}}
 
+% toggle use of symbol fonts.
+\@initializeif{\if@symbols}\@symbolsfalse
+\DeclareOption{symbols}      {\@symbolstrue}
+\DeclareOption{nosymbols}    {\@symbolsfalse}
+
 \DeclareOption*{}% avoid choking on unknown options
-\ExecuteOptions{right}
+\ExecuteOptions{right,symbols}
 \ProcessOptions*\relax% \ProcessOptions* processes the options in the order provided (i.e., with the later ones possibly overriding the former ones), while \ProcessOptions processes them in the order of the package
 
 %-------------------------------------------------------------------------------
@@ -30,17 +35,20 @@
 %  \setsansfont{Latin Modern Sans}
 %  \setmathfont{Latin Modern Math}
 %\else
-  \IfFileExists{lmodern.sty}%
-    {\RequirePackage{lmodern}}%
-    {}
+%   \IfFileExists{lmodern.sty}%
+%     {\RequirePackage{lmodern}}%
+%     {}
 %\fi
 
 % symbols
-\RequirePackage{ifxetex}
-\ifxetexorluatex
-  \moderncvicons{awesome}
+\if@symbols
+    \ifxetexorluatex
+    \moderncvicons{awesome}     % use font-awesome symbols if lualatex or xelatex is used
+    \else
+    \moderncvicons{marvosym}    % use marvosym symbols pdflatex is used
+    \fi
 \else
-  \moderncvicons{marvosym}
+    \moderncvicons{letters}    % do not use symbols, use letters
 \fi