Nested Tabs are broken

[aCuria]

This used to work in the old format: {{< tabs "" >}}

`## Tabs

{{% tabs %}}

{{% tab "a" %}}
Content for tab "a"

{{% tabs %}}
{{% tab "1" %}}
Content for tab a1
{{% /tab %}}
{{% tab "2" %}}
Content for tab a2
{{% /tab %}}
{{% /tabs %}}

{{% /tab %}}

{{% tab "b" %}}
Content for tab "b"
{{% tabs %}}
{{% tab "1" %}}
Content for tab b1
{{% /tab %}}
{{% tab "2" %}}
Content for tab b2
{{% /tab %}}
{{% /tabs %}}
{{% /tab %}}

{{% /tabs %}}`

[alex-shpak]

Hi!
I see, it got broken here, during simplification
f8a0e89

I will think how to fix it

[alex-shpak]

After checking around, it got broken here: #649
Need to figure how to get it better ID generation

[alex-shpak]

Pushed a change, use id for tab {{% tabs "nested-1-or-something" %}} for them.