Add paragraph alignment setting (justify/left/center/right) (#191)

## Summary

* **What is the goal of this PR?** 

Add a new user setting for paragraph alignment, instead of hard-coding
full justification.

* **What changes are included?**

One new line in the settings screen, with 4 options
(justify/left/center/right). Default is justified since that's what it
was already. I personally only wanted to disable justification and use
"left", but I included the other options for completeness since they
were already supported.

## Additional Context

Tested on my X4 and looks as expected for each alignment.

Co-authored-by: Maeve Andrews <maeve@git.mail.maeveandrews.com>

lib/Epub/Epub/parsers/ChapterHtmlSlimParser.h

@@ -33,6 +33,7 @@ class ChapterHtmlSlimParser {
   int fontId;
   float lineCompression;
   bool extraParagraphSpacing;
+  uint8_t paragraphAlignment;
   uint16_t viewportWidth;
   uint16_t viewportHeight;
 
@@ -46,7 +47,8 @@ class ChapterHtmlSlimParser {
  public:
   explicit ChapterHtmlSlimParser(const std::string& filepath, GfxRenderer& renderer, const int fontId,
                                  const float lineCompression, const bool extraParagraphSpacing,
-                                 const uint16_t viewportWidth, const uint16_t viewportHeight,
+                                 const uint8_t paragraphAlignment, const uint16_t viewportWidth,
+                                 const uint16_t viewportHeight,
                                  const std::function<void(std::unique_ptr<Page>)>& completePageFn,
                                  const std::function<void(int)>& progressFn = nullptr)
       : filepath(filepath),
@@ -54,6 +56,7 @@ class ChapterHtmlSlimParser {
         fontId(fontId),
         lineCompression(lineCompression),
         extraParagraphSpacing(extraParagraphSpacing),
+        paragraphAlignment(paragraphAlignment),
         viewportWidth(viewportWidth),
         viewportHeight(viewportHeight),
         completePageFn(completePageFn),