Implementing GcalWeekView to match the mockups.

What to say about this commit.
There's just one FIXME in gcal-week-view.c, about the size/width of the
GtkScrollbar used. That should not be hardcoded.
Also the background color applied to the scrollbar through css-theming might be
better placed inside the code, since the effectis part of the view.
About this view is still missing a way of signaling the current day. We are on
it, yet.

data/gtk-styles.css

@@ -40,6 +40,7 @@
 
 .calendar-view header {
   font: bold 12;
+  background-color: @theme_bg_color;
 }
 
 .calendar-view {
@@ -47,6 +48,7 @@
   font: 10;
 }
 
+
 .calendar-view:selected {
   color: #0C73E5;
   font: bold;
@@ -68,6 +70,15 @@
   border-radius: 0;
 }
 
+.scrollbar.slider {
+  background-color: alpha (@scrollbar_slider, 0.5);
+  border: #6e6e6e 1px solid;
+}
+.scrollbar.trough {
+  background-color: transparent;
+  background-image: none;
+}
+
 .entry {
   border-radius: 0;
 }

doc/Drawing

@@ -18,3 +18,53 @@ Month View
 | f  |                       |
 | t                          |
 |    |                       |
+
+Week View
+
++--------------------
+|  l | padding.top
+|- e -   -   -   -   -
+|  f |July 13, 2021
+|- t -   -   -   -   -
+|      top    | l |
+|-   -   -   -  e -   -   -   -
+|             | f |Sun
+|-   -   -   -  t -   -   -   -
+|      top    |   |
+|-   -   -   -+-----------------+
+|             |                 |
+|             | All-day event   |
+|             |                 |
+|             |                 |
+|-------------------------------+
+|    | top  r |        ^        |
+|-   -   -| i |        |        |
+| l  |9 AM  g |   cell_height   |
+| e       | h |        v        |
+| f  |--------+-----------------+
+| t           |                 |
+|    |        |                 |
+
+Notes: cell_height is equal to: padding.top + padding.bottom + 3*font_height
+
+Week View Grid
+
++----------------+--------------------
+|  Midnight      |
+|                |
+|                +- - - - - - - - - - -
+|                |
+|                |
++-------------------------------------
+|  1:00 AM       |
+|                |
+|                +- - - - - - - - - - -
+|                |
+|                |
++-------------------------------------
+|  2:00 AM       |
+|                |
+|                +- - - - - - - - - -
+|                |
+|                |
++-------------------------------------

src/Makefile.am

@@ -64,6 +64,7 @@ gnome_calendar_LDFLAGS =                                  \
   -Wl,--export-dynamic
 
 gnome_calendar_LDADD =                                    \
+  -lm                                                     \
   $(CALENDAR_LIBS)
 
 ENUM_TYPES =                                              \