Image stuff (#77)

Features
---------
Image to PDF supports multiple images, stretching and auto rotation
File inputs now only search for wanted file type
Settings now has a zip range so it can zip if you have more than x downloads (default 4)

extras
---------
DevTools support for easier development
Fix for temporary files for thread safety

src/main/resources/templates/convert/pdf-to-img.html

@@ -16,7 +16,7 @@
                         <h2 th:text="#{pdfToImage.header}"></h2>
                         <p th:text="#{processTimeWarning}"></p>
                         <form method="post" enctype="multipart/form-data" th:action="@{pdf-to-img}">
-                            <div th:replace="~{fragments/common :: fileSelector(name='fileInput', multiple=false)}"></div>
+                            <div th:replace="~{fragments/common :: fileSelector(name='fileInput', multiple=false, accept='application/pdf')}"></div>
                             <div class="form-group">
                                 <label th:text="#{pdfToImage.selectText}"></label> 
                                 <select class="form-control" name="imageFormat">