Bug 29066: Remove text in OPAC search form and use Font Awesome icons

Bug 29066: Remove text in OPAC search form and use Font Awesome icons

In modern front-end websites, first think you see in header region is an large input text with a search icon.
No need to say it is a search form.
We still tell it in 'title' attribut for accessibility.

This patch removes 'Search' text.
If 'my library first' feature is enabled, shows a text in title of a
question mark icon.
In submit button, replaces 'Go' with a seach icon and add title
'Search'.

Test plan :
1)
1.1) Set system preferences :
  OpacAddMastheadLibraryPulldown to 'Add'
  SearchMyLibraryFirst to 'Don't limit'
1.2) Go to OPAC main page
1.3) You don't see 'Search' anymore
1.4) You see in submit button an icon
1.5) Move mouse over submit button to see tooltip text 'Search'
2)
2.1) Set system preferences :
  OpacAddMastheadLibraryPulldown to 'Don't add'
  SearchMyLibraryFirst to 'Limit'
2.2) Go to OPAC main page
2.3) Log in
2.4) You don't see text 'Search (in <library name>) only'
2.5) You see a question mark icon
2.6) Move mouse over submit button to see tooltip text 'Search (in <library name>) only'

Signed-off-by: Samu Heiskanen <samu.heiskanen@hypernova.fi>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>