Translations shoud be used instead of string literals

[NoNoNo]

In pages there are multiple untranslated texts, e.g.

https://github.com/getgrav/grav-plugin-login/blob/388f1adb594bbdf706cb892b6ecf15311aae1ed1/pages/login.md?plain=1#L2

https://github.com/getgrav/grav-plugin-login/blob/388f1adb594bbdf706cb892b6ecf15311aae1ed1/pages/login.md?plain=1#L42

https://github.com/getgrav/grav-plugin-login/blob/388f1adb594bbdf706cb892b6ecf15311aae1ed1/pages/forgot.md?plain=1#L2

https://github.com/getgrav/grav-plugin-login/blob/388f1adb594bbdf706cb892b6ecf15311aae1ed1/pages/forgot.md?plain=1#L20-L22

https://github.com/getgrav/grav-plugin-login/blob/388f1adb594bbdf706cb892b6ecf15311aae1ed1/pages/profile.md?plain=1#L2

https://github.com/getgrav/grav-plugin-login/blob/388f1adb594bbdf706cb892b6ecf15311aae1ed1/pages/profile.md?plain=1#L81

https://github.com/getgrav/grav-plugin-login/blob/388f1adb594bbdf706cb892b6ecf15311aae1ed1/pages/unauthorized.md?plain=1#L2

https://github.com/getgrav/grav-plugin-login/blob/388f1adb594bbdf706cb892b6ecf15311aae1ed1/pages/unauthorized.md?plain=1#L7

https://github.com/getgrav/grav-plugin-login/blob/388f1adb594bbdf706cb892b6ecf15311aae1ed1/pages/reset.md?plain=1#L2

https://github.com/getgrav/grav-plugin-login/blob/388f1adb594bbdf706cb892b6ecf15311aae1ed1/pages/reset.md?plain=1#L33-L35

https://github.com/getgrav/grav-plugin-login/blob/388f1adb594bbdf706cb892b6ecf15311aae1ed1/pages/register.md?plain=1#L2

https://github.com/getgrav/grav-plugin-login/blob/388f1adb594bbdf706cb892b6ecf15311aae1ed1/pages/register.md?plain=1#L58-L60

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And, en passant, there is a jump from H1 to H3 in this file:

https://github.com/getgrav/grav-plugin-login/blob/388f1adb594bbdf706cb892b6ecf15311aae1ed1/pages/reset.md?plain=1#L33-L35