updated table of contents and clients section

content/_index.en.md

content/_index.md

content/clients/_index.en.md

content/clients/_index.md

content/clients/android.en.md

content/clients/android.md

content/clients/browser.en.md

content/clients/browser.md

content/clients/desktop.en.md

content/clients/desktop.md

content/clients/ios.en.md

content/clients/ios.md

content/clients/mobile.en.md

content/clients/mobile.md

static/images/15_Element_Android1_de.jpg

static/images/15_Element_Android1_en.jpg

static/images/15_Element_Android2_de.jpg

static/images/15_Element_Android2_en.jpg

static/images/15_Element_Android3_de.jpg

static/images/15_Element_Android3_en.jpg