Correctly style the first tab (contentManager)

It would be nice to be able to style it using css (QTabBar::tab:first)
but I can't figure how :/

We need to :
- hardcore the size of the tabs using `tabSizeHint`.
- "deactivate" the tab button with `setTabButton`
- set the size of the icons.

Fix #73

resources/css/style.css

@@ -123,10 +123,6 @@ QTabWidget::pane {
 }
 
 QTabBar::tab {
-    min-width: 205px;
-    max-width: 205px;
-    min-height: 40px;
-    max-height: 40px;
     border: none;
     border-right: 2px solid #ccc;
     border-bottom: 2px solid #ccc;

src/tabbar.cpp

@@ -15,6 +15,7 @@ TabBar::TabBar(QWidget *parent) :
     setElideMode(Qt::ElideNone);
     setDocumentMode(true);
     setFocusPolicy(Qt::NoFocus);
+    setIconSize(QSize(30, 30));
     connect(this, &QTabBar::tabCloseRequested, this, &TabBar::closeTab);
     connect(this, &QTabBar::currentChanged, this, &TabBar::onCurrentChanged);
     auto app = KiwixApp::instance();
@@ -76,6 +77,7 @@ void TabBar::setContentManagerView(ContentManagerView* view)
     mp_stackedWidget->addWidget(mp_contentManagerView);
     mp_stackedWidget->show();
     addTab(QIcon(":/icons/kiwix/app_icon.svg"), "");
+    setTabButton(0, RightSide, nullptr);
 }
 
 WebView* TabBar::createNewTab(bool setCurrent)
@@ -152,6 +154,12 @@ QString TabBar::currentArticleTitle()
     return currentWidget()->title();
 }
 
+QSize TabBar::tabSizeHint(int index) const {
+    if (index)
+        return QSize(205, 40);
+    return QSize(40, 40);
+}
+
 void TabBar::triggerWebPageAction(QWebEnginePage::WebAction action, WebView *webView)
 {
     CURRENTIFNULL(webView);

src/tabbar.h

@@ -33,6 +33,7 @@ public:
     void triggerWebPageAction(QWebEnginePage::WebAction action, WebView* webView=nullptr);
     QString currentArticleUrl();
     QString currentArticleTitle();
+    virtual QSize tabSizeHint(int index) const;
 signals:
     void webActionEnabledChanged(QWebEnginePage::WebAction action, bool enabled);
     void currentZimIdChanged(const QString& zimId);