Add support for icons (#20)

Icon rendering must use platform-specific APIs which means it must be
duplicated for every supported OS.

Icon lookup is delegated to a separate thread in order to prevent
the system functions from blocking the runtime.

This is because if a Jolly entry location is on a network drive, the
icon lookup APIs can hang for a long period of time.

Buildscript checks that necessary packages are installed and gives a
warning if they are not

.github/workflows/ci.yml

@@ -40,6 +40,10 @@ jobs:
       with:
         toolchain: ${{ env.MSRV }}
 
+    - name: Install dependencies
+      run: sudo apt-get install -y --no-install-recommends shared-mime-info xdg-utils gnome-icon-theme
+      if: startsWith(matrix.os, 'ubuntu-')
+
     - name: Build
       run: cargo build --verbose
     - name: Run tests

.github/workflows/release.yml

@@ -35,6 +35,11 @@ jobs:
     - name: Checkout repository
       uses: actions/checkout@v3
 
+    - name: Install dependencies
+      run: sudo apt-get install -y --no-install-recommends shared-mime-info xdg-utils gnome-icon-theme
+      if: startsWith(matrix.os, 'ubuntu-')
+
+
     - name: Build release binary
       run: cargo build --verbose --release